Bacteriocins: Properties and potential use as antimicrobials

Abstract

A variety of bacteriocins originate from lactic acid bacteria, which have recently been modified by scientists. Many strains of lactic acid bacteria related to food groups could produce bacteriocins or antibacterial proteins highly effective against foodborne pathogens such as Staphylococcus aureus, Pseudomonas fluorescens, P. aeruginosa, Salmonella typhi, Shigella flexneri, Listeria monocytogenes, Escherichia coli O157:H7, and Clostridium botulinum. A wide range of bacteria belonging primarily to the genera Bifidobacterium and Lactobacillus have been characterized with different health‐promoting attributes. Extensive studies and in‐depth understanding of these antimicrobials mechanisms of action could enable scientists to determine their production in specific probiotic lactic acid bacteria, as they are potentially crucial for the final preservation of functional foods or for medicinal applications. In this review study, the structure, classification, mode of operation, safety, and antibacterial properties of bacteriocins as well as their effect on foodborne pathogens and antibiotic‐resistant bacteria were extensively studied.

Antimicrobial potential of bacteiocins in food preservation.

1. INTRODUCTION

There are a variety of antimicrobial substances produced by living organisms as part of their immune reactions or defense mechanisms, which may enhance their ability to compete for space and resources. Especially, the production of antimicrobial substances such as hydrogen peroxide, fatty acids, organic acids, ethanol, lytic enzymes, antibiotics, and bacteriocins by living organisms is well evidence of their microbial antagonism. ¹ , ² , ³ Bacteriocins are a very heterogeneous class of bactericidal peptides or proteins produced by bacteria and archaea. ³ The vast majority of all bacterial species appear to be able to produce at least one bacteriocin, most of which are unknown. ⁴ Bacteriocins exhibit antibacterial activity and a specific immunity mechanism toward strains closely related to the producer bacteria. ³ , ⁴ This immunity is usually associated with a specific protein encoded in the bacterial genome (bacteriocin operon). ⁵ , ⁶ Almost all bacteriocins are small cationic molecules with hydrophobic or amphiphilic characteristics, which exhibit a narrow to broad inhibitory activity against closely related and non‐related species. ⁷ , ⁸ Bacteriocins may be secreted by both Gram‐positive and Gram‐negative bacteria. In particular, among Gram‐positive bacteria, bacteriocins derived from lactic acid bacteria are of great interest (LAB). ⁹ Lactic acid bacteria are a miscellaneous group of acid‐tolerant, facultative anaerobes, and fermentative organisms that possess generally regarded as safe (GRAS) and qualified presumption of safety (QPS) status. Therefore, their bacteriocins are regarded as safe by the USFDA (the U.S. Food and Drug Administration). ² , ⁵ , ¹⁰ LAB‐secreted bacteriocins are heat‐stable, proteases‐sensitive, ribosomally synthesized, and antimicrobial peptides, which either undergo or do not undergo enzymatic post‐translational modification process. ² , ⁴ , ⁶ , ⁹ , ¹¹ They are very diverse in terms of length, genetic origin, biochemical features, molecular weight (MW), cellular receptors, and interaction with the immune system. ⁵ , ⁹ , ¹² So far, many bacteriocins have been widely identified with various modes of action as follows: inducing cytoplasmic membrane permeability (by pore formation), inhibiting cell wall biosynthesis, and interfering with metabolic pathways. ¹ , ⁶ Membrane pore formation as a common inhibitory mechanism, high inhibitory activity with low concentrations in the nanomolar range, and relatively narrow‐spectrum antimicrobial activity are the characteristics of many LAB‐derived bacteriocins. ¹ During the last decade, LAB bacteriocins have received a great deal of attention due to their high potential, especially as natural food preservatives and novel therapeutic antibiotics, which have made them attractive for various applications. ¹³ In particular, numerous studies have been published in recent years, suggesting that bacteriocins may be used as an alternative to antibacterial agents in the prevention or treatment of bacterial infections. ¹⁰ Despite the long history of bacteriocins usage, there is no report about the development of bacterial resistance to bacteriocins. Some possible reasons may be as follows: having a fast pore‐formation mechanism, being easily degraded by proteolytic enzymes, and having a shorter biological half‐life in the human body or in natural environments; these factors minimize the possibility of interaction between bacteriocins and bacteria, as a starting point in the development of antibiotic resistance. ¹³ The most significant property that further enhances bacteriocins functional potential compared with conventional antibiotics is stability in a wide range of physicochemical conditions. In addition, due to their primary metabolite nature, bacteriocins also have other features such as genetic amenability through bioengineering to increase their activity/specificity against target bacterial pathogens and antibiotic‐resistant strains. ¹³ Lastly, bacteriocins modulate the host immune responses (as signaling peptides), and they have no destructive effect on commensal bacteria and low/no cytotoxicity against eukaryotic cells (more specifically to target cells). ³ , ¹⁴ Comparison of bacteriocins and antibiotics in terms of mode of action and physicochemical properties, especially the mechanism of resistance development (used by bacteria), provides evidence of the need for alternative antimicrobial compounds to combat bacterial infections. Bacteriocins have the potential to be used as ideal candidates. ¹⁰

In recent years, several studies have shown the protective effects of LAB bacteriocins on the gastrointestinal tract via eliminating pathogens or supporting the gut from bacterial colonization. ² They have also demonstrated the inhibitory ability of bacteriocins against intestinal pathogens such as Listeria monocytogenes, Salmonella enteritidis, Clostridium difficile, Staphylococcus aureus, and vancomycin‐resistant enterococci (VRE). ¹⁴ Moreover, in clinical applications, some bacteriocins have been shown to be highly effective in treating infections, especially those caused by multidrug‐resistant (MDR) strains. ¹³ Given the harmful effect of antibiotics on intestinal microbiota and the importance of gastrointestinal infections in human health, it seems that LAB‐derived bacteriocins could be considered as a promising antibiotic in the treatment of intestinal infections. ² This research aimed to review the literature regarding the properties of bacteriocins as a substitute for antibiotic therapy, their antibacterial effects on foodborne pathogens, their impact on antibiotic‐resistant bacteria, and the identification and extraction of new bacteriocins against intestinal pathogens.

2. THE BIOLOGY OF BACTERIOCINS

Bacteriocins were first identified almost 100 years ago as cationic, ribosomally synthesized, antimicrobial peptides, which act through forming pore and disrupting target cell membrane integrity, eventually leading to cell death. Lactic acid bacteria (LAB), in particular, are known to produce a variety of bacteriocins with characteristics that make them ideal for use in inactivating pathogens, including their broad antimicrobial activity spectrum, pH‐ and heat‐tolerance, and non‐toxic nature. In addition, LAB bacteriocins are sensitive to digestive proteases such as pancreatic complex, host proteases, trypsin, and chymotrypsin; thus, they do not adversely affect the gut microbiota. ¹⁵ According to Klaenhammer, ¹⁶ 99% of all bacteria probably produce at least one bacteriocin, most of which have not yet been identified because few researchers have looked for them. Most bacteriocins have two main characteristics that distinguish them from traditional antibiotics: Bacteriocins are ribosomally synthesized and have a relatively narrow‐spectrum antimicrobial activity. ¹⁷ Bacteriocins are a family of proteins that could be classified into two classes based on their size, microbial target, mode of action, release, and immunity mechanisms, including bacteriocins of Gram‐negative and Gram‐positive bacteria. ¹⁸ Bacteriocins may represent a good potential for use as substitutes for antibiotics with no side effects. Bacteriocins may have different modes of action, including inhibition of cell wall synthesis, inhibition through DNase and RNase activities, and more commonly, formation of pores in the target cell membrane. Lactic acid bacteria are ideal candidates for bacteriocin production in order to biocontrol of some bacterial species as they have a long history of safe use in the food industry. ¹⁹ Inoculation of food with bacteriocin‐producing strains and addition of purified or semi‐purified bacteriocins, which promote either a bactericidal effect with/without cell lysis or a bacteriostatic effect inhibiting cell growth, are the most common approaches to using bacteriocins for food biopreservation. ²⁰ Most LAB bacteriocins, especially those inhibiting Gram‐positive bacteria, exert their antimicrobial effects by targeting bacterial cell envelope. ²¹

3. WHAT ARE THE SOURCES OF BACTERIOCINS?

Antimicrobial peptides are natural and unique antibiotic substances produced by different microorganisms, mammals, plants, and insects. ²² , ²³ Bacteriocin‐producing bacteria could be extracted from various sources such as water, soil, animal intestines, and food products, which are defined as unconventional sources, while the human gastrointestinal tract is considered as the conventional source of bacteriocin producers. Understanding more about unconventional sources, especially food products ²⁴ , ²⁵ and animals, ²⁶ has become interesting for researchers in recent years. Bacteriocin‐producing bacteria in the GIT include Lactobacillus, Enterococcus, Streptococcus, and Staphylococcus. ²⁴ These bacteria could help the skin serve as the first line of body's defense against pathogens. In addition to inhibiting the growth of other bacteria, these bacteriocins as mediator molecules are able to help the immune system. ²⁷ , ²⁸ , ²⁹ , ³⁰

4. UNCONVENTIONAL SOURCES OF BACTERIA THAT PRODUCE BACTERIOCIN

• 4.1 In dairy products, the most common LAB strains include Lactococcus lactis and L. plantarum in camel and goat milk, L. plantarum in cheese, L. kefiranofaciens in kefir, and S. thermophilus, and L. brevis LSe in other dairy products. In dairies such as milk of different origins, L. brevis produces bacteriocin with antibacterial activity. Brevibacillus brevis and Bifidobacterium lactis are the most common LAB in raw milk, while L. acidophilus is the most common LAB in yogurt and fermented soy products. ³¹ Generally, Lactococcus, Lactobacillus, and Streptococcus are the predominant probiotic bacteria in milk products. ³²
• 4.2 L. plantarum subsp. plantarum, Pediococcus pentosaceus, L. brevis, L. curvatus, and L. fermentum are the most widely used bacteriocin‐producing bacteria in fermented raw‐meat products (like sausage); E. faecium UAM1 is the most common LAB in cooked meat products, while L. plantarum, L. brevis, and P. pentosaceus strains are common in other fermented meat products. ²⁵ , ³³ These LAB strains exhibit inhibitory activity on L. monocytogenes, Aeromonas hydrophila, and S. aureus and prevent the growth of these foodborne pathogens. ³⁴ , ³⁵ , ³⁶
• 4.3 The most common LAB strains in seafood are L. brevis LAP2, L. plantarum, and E. faecium HL7. ²⁶ It has been proved that LAB strains in fish and shrimp show antibacterial activity against foodborne pathogens and other bacteria. ³⁷ A. hydrophila as a common freshwater fish pathogen could be significantly inhibited by probiotic activity of bacteriocin‐producing pathogens in fish gut. ³⁸ In a study, LAB isolated from the intestine of a fish named Mugil cephalus showed inhibitory function against fish and even human pathogens. ³⁹
• 4.4 L. brevis, Lactiplantibacillus pentosus, Lacticaseibacillus paracasei. Lacticaseibacillus plantarum, Limosilactobacillus fermentum, Lactobacillus, Weissella, Pediococcus, and E. durans are the most important LAB in fruit and vegetables (raw fruits and vegetables, carrots, pineapple, and different fruits). ³²

Some bacteria residing in the sea or ocean, such as Aeromonas, Alteromonas, and Vibrio, are capable of exhibiting a strong bactericidal effect on drug‐resistant bacteria and boosting the immune system by producing bacteriocin. ³⁰

5. BACTERIOCINS PRODUCED BY LACTIC ACID BACTERIA

Bacteriocins, as a group of diverse antimicrobial peptides, are known as an inhibitory agent against closely related organisms such as Gram‐positive and Gram‐negative bacteria, they are produced by various bacterial species, specifically lactic acid bacteria (LAB). ⁵ , ⁴⁰ , ⁴¹ It has also been well documented that LAB strains are commonly involved in a broad spectrum of ecological niches and include various genera, such as Pediococcus, Leuconostoc, Weissella, Lactococcus, Lactobacillus, Streptococcus, Enterococcus, Carnobacterium, Propionibacterium, Aerococcus, Tetragenococcus, Oenococcus, and Bifidobacterium. ⁴⁰ , ⁴² Bacteriocins could be categorized into three major classes. Class I bacteriocins are small post‐translationally modified peptides, which are/could be further subdivided into Class Ia (lantibiotics), Class Ib (labyrinthopeptins), and Class Ic (sanctibiotics). ⁴³ Nisin is a Class I bacteriocin. Class II bacteriocins are small, heat‐stable, non‐modified peptides described as unmodified bacteriocins, which could be further subdivided into Class IIa (pediocin‐like bacteriocins), Class IIb (two‐peptide unmodified bacteriocins), Class IIc (circular bacteriocins), and Class IId (unmodified, linear, non‐pediocin‐like bacteriocins). In addition, Class III bacteriocins as larger peptides (>10 kDa, heat‐labile) are subdivided into two subclasses, namely IIIa (lysostaphin and enterolysin A) or bacteriolysins and IIIb. ⁴² , ⁴⁴ , ⁴⁵ Bacteriocins are commonly named based on the genus or species of producer strain. For instance, lacticin and nisin are produced by Lactococcus spp., enterocin by Enterococcus spp., pediocin by Pediococcus spp., leucocin by Leuconostoc spp., etc. ⁴⁰

6. BIOSYNTHESIS AND POTENTIAL APPLICATION OF LAB BACTERIOCINS

There are some factors affecting the production of bacteriocins, such as culture conditions and the type of microbial strain. Bacteriocins are post‐translationally modified and ribosomally synthesized peptides that are initially produced as inactive pre‐peptides and then converted into an active form. ⁵ , ⁴⁶ After transport and cleavage of produced pre‐peptides, they are converted into mature (active) bacteriocins. Depending on the type of bacteriocins, genes responsible for pre‐peptides transport and modification are located close to the bacteriocin biosynthesis gene, and genes responsible for the immunity and active bacteriocin production are broadly located in operon clusters and might be harbored in plasmid, genome, or other mobile genetic factors. ⁴⁷ In addition to inducible expression, these operons require auto‐inducer peptides to induce bacteriocin production. The regulation of expression is generally fulfilled by a two‐part regulatory system, but in some cases, this process is done by three‐element ones. The production of bacteriocins is fulfilled in the exponential growth phase by retaining a line‐to‐line connection to the biomass production. ⁴⁴

7. ACTIVITY OF LAB AGAINST FOODBORNE PATHOGENS

According to the FDA, the most prevalent foodborne pathogenic bacteria are as follows: L. monocytogenes, S. enteritidis, Shigella, S. typhimurium, pathogenic Escherichia coli, Campylobacter jejuni, C. perfringes, and S. aureus. ⁴¹ Due to some restrictions on the use of therapeutic antibiotics in food production and processing as well as nontoxicity of treatment with LAB‐derived antimicrobial peptides, most research in recent years has been devoted to investigating these bacteriocins. Given the cleavage of bacteriocins by gastrointestinal proteases, reducing their activity level, they are generally safe and show a considerable capacity to constrain foodborne pathogens growth. ⁴¹ , ⁴⁸ Also, considering bacteriocins ability to form pores in the cell membrane of sensitive bacteria, they are naturally bactericidal or bacteriostatic. For instance, BMP11 as a new bacteriocin produced by L. crustorum against L. monocytogenes, has been shown to destroy cell membrane integrity and increase membrane permeability. ⁴⁹ Moreover, it has been well documented that P. acidilactici QC38 is able to inhibit L. monocytogenes, L. innocua, S. typhimurium, E. coli, V. cholerae NO 01, and V. cholerae O1 Ogawa. ⁵⁰ The inhibitory activity of Pediococcus spp. (isolated from cheese) against Listeria species was reported by Cavicchioli et al. ⁵¹ They indicated that bacteriocins produced by E. hirae ST57ACC and P. pentosaceus ST65ACC inhibited 100% of L. monocytogenes strains and two L. innocua strains. Nisin, produced by L. lactis subsp. Lactis, has been reported to inhibit the growth of Gram‐positive bacteria as well as Clostridium and Bacillus spores. Considering its antimicrobial activity against Listeria spp., pediocin (P. acidilactici) has been shown to mitigate the growth of spoilage microorganisms during storage in the meat industry as well as to be efficient against L. monocytogenes in beef, turkey, and sliced jambon. ⁴⁴ Similar to pediocin, the semi‐purified bacteriocin BacTN635 (produced by L. plantarum sp. TN635) has also been shown to be strongly active against spoilage microorganisms in chicken breast and beef. ⁵² Furthermore, the potency of combined application of various bacteriocins, including subclass IIa bacteriocins, L. fermentum ACA‐DC179, and bioprotective cultures of E. faecium PCD71, in inhibiting L. monocytogenes in various meat products has been documented. In addition to enterocins as broad‐spectrum antimicrobial bacteriocins against foodborne pathogens (Clostridium spp. and Listeria spp.), ⁴⁵ purified bifidocin A has also been indicated to display a broad range of antimicrobial activity against spoilage and foodborne pathogenic bacteria, such as S. aureus, L. monocytogenes, E. coli, and some types of yeasts. ⁵³

8. ARE BACTERIOCINS THE BEST SUBSTITUTE FOR ANTIBIOTIC THERAPY?

To the best of our knowledge, antibiotics play an important role in the disease prevention and treatment in animals and humans. In addition to adverse effects of some antibiotics, the emergence of antibiotic‐resistant, MDR (multidrug‐resistant), and XDR (extensively drug‐resistant) strains has recently become a major concern. ⁵⁴ , ⁵⁵ It is estimated that by 2060, at least 20 new antibiotics are needed to overcome the problem of antibiotic resistance, while the design of new antibiotics is a time‐consuming and slow procedure. ⁵⁶ Therefore, it is necessary to develop new treatment strategies that could eliminate antibiotic‐resistant microorganisms. ⁵⁷ One of the strategies is to use antimicrobial peptides to achieve this goal. Bacteriocin is considered as a suitable antimicrobial peptide due to its thermal stability and high efficacy with nano‐molecular size. ⁵⁸ , ⁵⁹ In addition to the immune system, bacteriocins are able to affect other bacteria through competition in colonization. ²¹ , ³³ Researchers are looking for anti‐pathogenic bacteriocins that are as effective as antibiotic therapy. ⁶⁰ Bacteriocins have been shown to possess advantages over antibiotics. ⁶¹ These antimicrobial peptides are considered to provide more protection with no side effects compared to antibiotics. A study examining the differences between bacteriocins and antibiotics found that oral administration of pediocin PA‐1 had no side effects on the gastrointestinal tract, while under the same conditions, the use of antibiotics such as penicillin and tetracycline exhibited different results. ⁶² Bacteriocins are synthesized ribosomally and considered as primary metabolites, while antibiotics are a type of secondary metabolites. This feature allows researchers to design novel bacteriocins with more effective capabilities using bioengineering techniques based on bacteriocins synthesis ways. ⁶³ Unlike antibiotic‐producing bacteria, bacteriocins are not inhibited by antimicrobial agents. The activity of bacteriocins on drug‐resistant strains, hospital‐acquired infections, respiratory tract infections, skin diseases, dental infections, vaginosis, and tuberculosis has been proved. ⁶² Several antibiotics are not active against infections caused by S. aureus, enterococci, and pneumococci strains. Studies have shown that MRSA (methicillin‐resistant S. aureus) and VRE (vancomycin‐resistant enterococci) are affected by bacteriocins such as nisin A and lacticin 3147. ⁶⁴ Nisin F and mersacidin were shown in a study to inhibit S. aureus growth as a respiratory pathogen without damaging the lungs and other respiratory organs such as bronchi and trachea in animal model. ⁶⁵ Proteolytic digestion of bacteriocins in the gastrointestinal tract may affect bacteriocins activity; however, it is possible to overcome the problem by their encapsulation and insertion into liposomes. ⁶³ Also, the use of synergistic function of bacteriocins is economically more cost effective than producing expensive antibiotics. ⁶³ The inherent resistance of certain bacteria to these peptides with very strong antimicrobial activity at nanomolar concentrations is one of the most challenging aspects of bacteriocins usage. Although few studies have examined resistance to bacteriocins, some studies have shown a nearly 10‐fold increase in nisin MIC against L. monocytogenes, indicating a 10‐fold increase in resistance to nisin. Degradation of nisin by B. cereus‐synthesized nisinase leads to inactivation of this bacteriocin, while bacitracin, polymyxin, and gramicidin are resistant to these enzymes. ⁶⁶ , ⁶⁷ Unlike widespread studies on enzymes mediating extensive resistance to β‐lactam antibiotics, such as β‐lactamases and carbapenemases, resistance of bacteriocin‐degrading enzymes has not been properly investigated. ⁶⁸ Therefore, there is controversy over whether bacteriocins could be considered as alternatives to antibiotics or not. Studies results describe bacteriocins as supplements for antibiotics due to their high stability, no side effects, and potential to induce a synergistic effect. ⁶⁹ In combination with antibiotics, bacteriocins act synergistically; they not only increase the efficiency of antibiotics and prevent the emergence of antibiotic‐resistant species but also reduce the side effects of antibiotics by lowering the concentration of antibiotics needed to eliminate bacteria. ⁶¹ , ⁶³ , ⁷⁰ , ⁷¹ Nowadays, the therapeutic efficacy of bacteriocins could be enhanced by designing engineered bacteriocins; this requires biological and chemical modification methods and further investigations. ⁵⁷

9. IMPACT OF BACTERIOCINS ON ANTIBIOTIC RESISTANCE PROFILE OF DRUG‐RESISTANT BACTERIA

The incidence of antibiotic resistance is attributed to several factors, including overuse of antibiotics, self‐medication at home, and improper antibiotic administration. When people consume contaminated food with such drug‐resistant bacteria, they lose sensitivity to the relevant antibiotics. ⁷² According to available information, many patients die due to antibiotic resistance with an annual rate of at least 700,000 cases, and this number is likely to increase by 2050. Some bacteriocins such as nisins A and F, mersacidin, mutacin 1140, lactacin 3147, and pediocin AcH/PA‐1 are active against MRSA and VRE strains. ⁶⁵ , ⁷³ , ⁷⁴ Brand et al. ⁷⁵ indicated that nisin F could inhibit S. aureus infection in mice and reported that the growth‐inhibition time lasted only 15 minutes. Another study by Fernández et al. (2008) demonstrated the antibacterial activity of nisin A in mastitis. They also described bacteriocins as efficient alternatives to antibiotics and showed that after two weeks, the number of bacteria in the milk of mothers with mastitis was significantly reduced and then followed by relief of symptoms. ⁷⁶ It has been shown that Bacillus spp. are able to reduce MRSA infection in animal model by producing mersacidin. ⁷³ Bacteriocin LipA is active against Pseudomonas aeruginosa and could eliminate resistant strains. Drug‐resistant S. aureus strains in goat milk are also affected by AS‐48 and nisin. These bacteriocins both individually and synergistically are able to eliminate S. aureus. ⁷⁷ Researchers have shown that B. subtilis KIBGE IB‐17 produces a heat‐resistant bacteriocin called BAC‐IB‐17 which is very effective against MRSA strains. ⁷⁸ Also, the effect of another bacteriocin called sonorensinon has been proven against various Gram‐positive bacteria, such as antibiotic‐resistant S. aureus biofilms and Gram‐negative bacteria. ⁷⁹ In an animal study in the field of bacteriocin design, bacteriocin peptide Ω76 was introduced as an active substance against carbapenem‐ and tigecycline‐resistant Acinetobacter baumannii. However, in this study, the relevant bacteriocin showed toxic effects such as nephrotoxicity, which was resolved in combination with antibiotics. ⁸⁰

10. IS IT POSSIBLE TO CONTROL FOODBORNE BACTERIA BY BACTERIOCINS?

Food pathogenic bacteria are present in both planktonic and biofilm forms as foodborne pathogens. In addition to being able to counteract with drug‐resistant bacteria, bacteriocins may also be used as food and dairy products preservatives. ⁸¹ According to studies, LAB‐derived bacteriocins such as nisin, pediocin PA‐1, pediocin, mersacidin, mutacin, and lacticin are mostly used in the food processing industry as preservatives that are capable of preventing the growth of C. botulinum, E. faecalis, VRE, L. monocytogenes, S. aureus, and other foodborne pathogens. ⁸² , ⁸³ , ⁸⁴ L. monocytogenes as the most common meat food pathogen could cause serious infections. Huang et al. ⁸⁵  showed that enterocin RM6 and enterocin AS‐48 as cyclic peptides generated by E. faecalis (found in raw‐milk) were able to affect some foodborne bacteria, especially L. monocytogenes, B. cereus, and MRSA strains. Studies have shown the effects of various bacteriocins on L. monocytogenes. ⁸² , ⁸⁶ , ⁸⁷ , ⁸⁸ B. cereus is another important foodborne pathogen causing different opportunistic infections in immunocompromised and immunocompetent individuals, such as food poisoning. Lauková et al indicated that lantibiotic bacteriocins, namely, gallidermin, and nisin, can be prevent from biofilm‐forming enterococci multiplication isolated by Slovak dry fermented meat. ⁸⁹ Draper et al. ⁹⁰  showed that lacticin 3147 as a lantibiotic in combination with polymyxin B could be active against B. cereus 8079 and B. cereus 5247. There are other bacteria known as foodborne pathogens that have been extensively studied by researchers to evaluate the effect of different bacteriocins on their growth and proliferation. For example, elimination of S. entrica serovar typhi following the use of nisin along with β‐lactam antibiotics was proven in a study by Rishi et al. ⁹¹ Although bacteriocins have become popular as an antimicrobial peptide in recent decades, ⁶² various studies have currently shown that bacteriocins in combination with conventional antibiotics could have a broader and stronger effect; however, the role of bacteria as an antimicrobial agent in the management of infections is still controversial.

11. CLASSIFICATION OF BACTERIOCINS

Up to now, four classes of LAB bacteriocins have been identified: Class I, known as lantibiotics, is composed of modified bacteriocins; Class II includes heat‐stable, minimally modified bacteriocins; Class III includes larger, heat‐labile bacteriocins; and Class IV is composed of complex bacteriocins with carbohydrate or lipid moieties. Classes I and II bacteriocins have been the focus of most probiotic research. ⁹² Lantibiotics are divided into three groups based on their structure and mode of action. Type A lantibiotics, such as nisin, are small (2–5 kDa) proteins with positively charged molecules, which kill bacteria via the formation of membrane pores, causing dissipation of membrane integrity and efflux of small metabolites from the sensitive cells. Mersacidin is a member of Type B lantibiotics that kill bacteria by interfering with cellular enzymatic reactions, such as cell wall synthesis. ⁹³ Another subgroup, such as lacticin 3147, is two‐component lantibiotics that synergistically display antimicrobial activity. It has been shown that dual activities could be distributed across two peptides: While one resembles Type B lantibiotic mersacidin that depolarizes the membrane, the other one is more similar to Type A lantibiotic nisin that acts through pore formation. Class II LAB bacteriocins are also small non‐lanthionine‐containing peptides that kill bacteria by inducing membrane permeability and the subsequent leakage of molecules from target bacteria. These bacteriocins are organized into the following subgroups: Class IIa is the largest group, including pediocin (this group is also called pediocin‐like bacteriocins), sakacin A, and leucocin A. Like Type A lantibiotics, Class IIa bacteriocins act through the formation of pores in the cytoplasmic membrane. Class IIa bacteriocins are distinguished by shared activity against Listeria and a conserved amino‐terminal sequence (YGNGVXaaC) that is thought to facilitate nonspecific binding to the target surface. Class IIb bacteriocins, such as lacticin F and lactococcin G, are composed of two different proteins; they form pores in the cell membrane to inhibit or kill their target bacteria. Class IIc bacteriocins are sec‐dependent, such as acidocin 1B. ⁹⁴ Class III bacteriocins are large, heat‐labile proteins such as helveticins J or lactacin B. Class IV bacteriocins such as leuconocin S and lactocin 27 require lipid or carbohydrate moieties for activity. ⁹⁵

11.1. Bacteriocins of Gram‐positive bacteria

Bacteriocins of Gram‐positive bacteria are as abundant as and even more diverse than those found in Gram‐negative bacteria. Bacteriocins of Gram‐positive bacteria, in general, and lantibiotics, in particular, require more genes for their production than those of Gram‐negative bacteria. The nisin gene cluster, for example, includes genes for encoding the pre‐peptide (nisA), modifying amino acids (nisB, nisC), cleavage of the leader peptide (nisP), secretion (nisT), immunity (nisI, nisFEG), and regulation of expression (nisR, nisK). These gene clusters are most often encoded on plasmids but are occasionally found on chromosomes. In several Gram‐positive bacteria, bacteriocins synthesis genes, including nisin, are located on transposons. ⁹⁶ Bacteriocins of Gram‐positive bacteria are restricted to eliminate other Gram‐positive bacteria. The range of their antimicrobial activity could vary significantly from relatively narrow spectrum, such as in lactococcins A, B, and M, which have been found to kill only Lactococcus, to extraordinarily broad spectrum, such as in some Type A lantibiotics including nisin A and mutacin B‐Ny266, which have been shown to kill a wide range of organisms, including Actinomyces, Bacillus, Clostridium, Corynebacterium, Enterococcus, Gardnerella, Lactococcus, Listeria, Micrococcus, Mycobacterium, Propionibacterium, Streptococcus, and Staphylococcus. Contrary to conventional wisdom, these particular bacteriocins are also active against a number of medically important Gram‐negative bacteria including Campylobacter, Haemophilus, Helicobacter, and Neisseria strains as well as methicillin‐resistant bacteria. ⁹⁷

11.1.1. Bacteriocins of Lactobacillus

The growing emergence of antibiotic‐resistant bacteria in the food industry needs to be controlled with effective antimicrobials. Plantaricin is one of the most important known bacteriocins produced by Lactobacillus. Lacticaseibacillus plantarum could produce at least six different bacteriocins. Several bacteriocin‐producing strains of L. plantarum are used in the food production. ⁹⁸ Zhang et al. (2018) in their study indicated that bacteriocin J23 produced by L. plantarum J23, isolated from Chinese traditional fermented milk products, showed thermal stability at temperatures below 100°C for 30 min, pH stability in the range of 2.0 to 12.0, and strong activity against L. monocytogenes. Their study results suggest that bacteriocin J23 have potential application prospects in the food industry. ⁹⁹ Díaz et al. ¹⁰⁰ demonstrated that plantaricin‐producing L. plantarum strain EC52 isolated from poto poto exhibited a strong inhibitory activity against L. monocytogenes and E. coli O157:H7 in meat. Omar et al. ¹⁰¹ indicated that bacteriocin‐producing L. plantarum C11 isolated from the Congolese fermented maize product poto poto exhibited inhibitory activity against S. enterica, E. coli, S. aureus, E. aerogenes, B. cereus, E. faecalis, and L. monocytogenes and could be used to improve the safety and storage stability of poto poto. Plantaricin JLA‐9 as a new bacteriocin was purified by Zhao et al. ¹⁰² and showed broad‐spectrum antibacterial activity against Gram‐positive and Gram‐negative bacteria, especially Bacillus spp. This bacteriocin could prevent the growth of B. cereus spores. ST28MS and ST26MS bacteriocins produced by two different strains of L. plantarum were purified in a study from molasses and showed inhibitory activity against Gram‐negative bacteria, including P. aeruginosa, E. coli, and A. baumannii. ¹⁰³ Two bacteriocins JW3BZ and JW6BZ produced by L. plantarum (isolated from Bulgarian boza) were shown to be active against a wide range of Gram‐positive bacteria by Von Mollendorff et al. ¹⁰⁴ Also, plantaricin C‐11, ¹⁰⁵ plantaricin NA, ¹⁰⁶ and bacteriocin AMA‐K have been shown to have a strong anti‐Listeria activity and therefore may be used in food preservation in the future. ¹⁰⁷ , ¹⁰⁸ Amortegui et al. ¹⁰⁹ presented the characteristics of bacteriocins produced by L. plantarum LE5 and LE27 isolated from ensiled corn with antimicrobial activity against L. monocytogenes, L. innocua, and E. faecalis. L. plantarum strain LR/14 identified by Tiwari et al. ¹¹⁰ was characterized to produce a bacteriocin inhibiting L. monocytogenes, S. aureus, and urogenic E. coli. Song et al. ¹¹¹ indicated that plantaricin ZJ5 (PZJ5) produced by L. plantarum ZJ5 with a molecular weight of 2572.9 Da had strong activity against S. aureus. The antimicrobial activity of nine bacteriocins (ET05, ET06, ET12, ET30, ET31, ET32, ET34, ET35, and ET88) of bacteriocin‐producing LAB isolated from vacuum‐packaged cold‐smoked salmon (CSS) was determined against S. aureus, E. faecalis, L. monocytogenes, and E. faecium in a study by Tome et al. ¹¹² In their study, bacteriocin ET06 belonging to the Class IIa bacteriocins inhibited 84.2% of 19 Listeria strains. The highest anti‐Listeria activity was recorded for ET05, ET30, and nisin derived from L. lactis subsp. lactis ATCC 11454. ¹¹² In another study in 2015, bacteriocins produced by L. curvatus MBSa2 (sakacin P) and L. curvatus MBSa3 (sakacin X) were shown to have inhibitory activity against L. monocytogenes strains. Bacteriocin produced by L. curvatus MBSa2 caused a 2 and 1.5 log reduction in the count of L. monocytogenes in the salami after 10 and 20 days, respectively, suggesting that application of these bacteriocins could be an additional measure to improve the safety of these ready‐to‐eat products with regards to L. monocytogenes. ¹¹³ In a study by Mokoena (2017), bacteriocins ST22Ch, ST153Ch, and ST154Ch, produced by L. sakei strains (ST22Ch, ST153Ch, and ST154Ch) isolated from Salpicao, were shown to have inhibitory activity against Listeria spp., Enterococcus spp., Klebsiella spp., E. coli, Pseudomonas spp., Staphylococcus spp., and Streptococcus spp. Maximum activity of these bacteriocins was recorded during the early stationary phase. All sakacins belonged to the Class IIa bacteriocins and possessed strong antilisterial activity. Bacteriocins ST22Ch, ST153Ch, and ST154Ch were produced at high levels during all phases of (fermented) meat processing. The spectrum of antibacterial activity of these strains (ST22Ch, ST153Ch, and ST154Ch) indicates their potential application in a mixed starter culture for the fermentation of meat products. ⁵ Sivakumar et al. ¹¹⁴  showed that bacteriocin of L. acidophilus (isolated from milk) inhibited the growth of foodborne pathogens, such as V. cholerae, S. typhi, Shigella spp., B. cereus, S. aureus, E. coli, and E. faecalis. In a study by Yi et al. (2016), bacteriocin MN047A (BMA) was found to have antibacterial activity against multidrug‐resistant bacteria and broad‐spectrum inhibitory activity against both Gram‐positive and Gram‐negative bacteria, such as E. coli and S. aureus. This bacteriocin was produced by L. crustorum MN047, which was first isolated from koumiss. ¹¹⁵ In another study by Jiang et al. (2017), a novel bacteriocin called pentocin JL‐1 was produced by L. pentosus; this bacteriocin showed a broad‐spectrum inhibitory activity against both Gram‐positive and Gram‐negative bacteria, especially multidrug‐resistant S. aureus. These results suggest that pentocin JL‐1 has the potential to be used as a biopreservative in the food industry. ¹¹⁶ Zhu et al. (2000) isolated bacteriocin‐producing L. gasseri strain KT7 from infant feces. The bacteriocin gassericin KT7 showed inhibitory activity against some pathogenic bacteria including Listeria, Clostridium, and Enterococcus. This bacteriocin was produced constitutively during exponential growth phase. ¹¹⁷ Another bacteriocin, produced by L. viridescence, was identified by Kp et al. ¹¹⁸ for use in the preservation of various food products with strong antibacterial properties. For the first time, Gautam et al. (2015) reported bacteriocin‐producing potential of L. spicheri strains. Bacteriocin of L. spicheri G2 showed strong activity against pathogenic bacteria such as S. aureus, L. monocytogenes, C. perfringens, S. mutans, L. mesenteroides, and B. cereus. Maximum activity of this bacteriocin (2000 AU/ml) was recorded in MRS broth at 35°C and pH 4.0 after 34 h. ¹¹⁹ L. acidophilus produces Class II acidocin CH5 with a restricted activity against Gram‐positive bacteria. Deraz et al. ¹²⁰ identified another bacteriocin designated as acidocin D20079, produced by L. acidophilus DSM 20079, with a low molecular weight (6.6 kDa), extreme pH‐ and heat‐stability, and narrow‐spectrum inhibitory activity. Table 1 summarizes the classification of bacteriocins with few examples.

TABLE 1.

Bacteriocins of Lactobacillus and their main characteristics

Bacteriocin	Species and strain	Source	Mol. wt. (kDa)	Heat‐stability range	Sensitivity	PH Stability range	Production phase	Optimal production	Inhibitory‐activity spectrum	Reference
ET05, ET12, ET32, ET34,	L. delbrueckii	Cold‐smoked salmon	3.5	At 60°C for 60 min, and at 100°C for 20 min.	Proteolytic enzymes (pepsin A)	2–8	MRS broth with 0.4% DL‐threonine at 30°C	Heat: 37°C PH: 6.5	L. monocytogenes	112
ET06, ET30, ET31,	L. curvatus	Cold‐smoked salmon	2.8–4.5	At 60°C for 60 min, and at 100°C for 20 min.	Proteolytic enzymes (pepsin A)	2–8	MRS broth with 0.4% DL‐threonine at 30°C	Heat: 37°C PH: 6.5	L. monocytogenes	112
Bacteriocins MBSa2 and MBSa3	L. curvatus	Salami	2–4	At 25 and 37°C for 8 h, at 30°C for 6 h, and at 121°C for 15 min	Proteolytic enzymes: a‐chymotrypsin Streptomyces griseus protease type XIV Trypsin Pepsin Proteinase K	2–10	MRS agar at 37°C for 24 h	Heat: 37°C PH: 6–8	L. monocytogenes	113
Fermenticin HV6b	L. fermentum HV6b MTCC 10770	Human vaginal ecosystem	(−)	(−)	(−)	(−)	MRS supplemented with 0.1% w/v Tween 80, at pH 6.5 and 37°C	(−)	B. fragilis B. ovatus B. vulgatus C. albicans C. sporogenes E. coli E. faecalis G. vaginalis K. pneumoniae L. mesenteroides L. monocytogenes M. flavus N. gonorrhoeae N. mucosa P. aeruginosa P. mirabilis Staphylococci Streptococci S. typhi V. cholerae	121
Nisin	L. lactis subsp. lactis ATCC 11454	Milk and traditional Sardinian cheese		At 121°C for 15 min		2.5–9			L. monocytogenes C. difficile S. pneumoniae E. faecalis S. bovis S. aureus	122
ST22Ch,	L. sakei	Pork product	3.0	At 30–100°C for 2 h	Proteolytic enzymes: Proteinase K Pronase Trypsin Pepsin Papain	2–10	MRS agar at 30°C for 24 h		Enterococcus spp. Listeria spp. E. coli Klebsiella spp. Pseudomonas spp. Staphylococcus spp. Streptococcus spp.	123
Bacteriocin MN047	L. crustorum MN047	Koumiss from Xinjiang	1.77	Up to 121°C for 30 min	Protease	2–11	MRS agar at 37°C for 48 h		S. aureus E. coli	115
Bacteriocin GM3	L. sakei GM3	Goat milk	4.8	At 75°C for15 min, at 85°C for 15 min, at 85°C for 30 min, and at 100°C for 20 min	Pepsin Trypsin Papain Proteinase K	2–10	MRS medium at 37°C		P. aeruginosa MTCC 741 S. aureus MTCC 3160	124
Plantaricin	L. plantarum strain EC52	Poto, an ethnic maize fermented food	(−)	(−)	(−)	(−)	MRS Spain at 30°C		L. monocytogenes E. coli O157:H7	125
Plantaricin JLA−9	L. plantarum JLA−9	Suan‐Tsai	1.04	At 121°C for 20 min	α‐chymotrypsin Pepsin Alkaline protease Papain	2–7	MRS 92 medium at 37°C		Bacillus spp.	102
Gassericin KT7	L. gasseri KT7	Infant feces	5	At 100 °C for 30 min, and at 121°C for 30 min	Proteinase K Trypsin Chymotrypsin ®cin Papain	2–10	MRS broth at 35°C for 34 h	Heat: 30–70°C PH: 4–7	C. perfringen C. botulinum S. aureus L. monocytogenes E. facecalis B. cereus	117
Pentocin JL−1,	L. pentosus	Grey carpet shark	2.9	At 120°C for 15 min	Proteinase K Trypsin Pepsin Alkaline protease	5–7	MRS at 30 ∘C for 24 h	Heat: 30°C PH: 5–6	Multidrug‐resistant S. aureus	116

11.1.2. Bacteriocin of Enterococcus

Enterococcus is the third main genus of lactic acid bacteria (LAB) after Lactobacillus and Streptococcus. ¹²⁶ They are ubiquitous bacteria of human and animal gastrointestinal tracts, which are also present in vegetables, meat, milk, and cheese. ¹²⁷ Their ability to colonize such diverse ecological niches is related to their tolerance in harsh environmental conditions. ¹²⁸ Despite concerns about their existence as important opportunistic pathogens causing a wide variety of infections, they could exhibit interesting functions. Purification and genetic characterization of many enterococci‐derived peptide bacteriocins have been reported, most of which have been obtained from E. faecalis and E. faecium (Table 2). Since some of these bacteriocins could not be grouped with typical LAB‐derived bacteriocins according to traditional classification, enterocins classification into four new classes has been proposed. ¹²⁹ Cytolysin produced by E. faecalis is a two‐linear peptide lantibiotic with cytolytic (hemolytic) activity, and its encoding genes are found in both hospital and food isolates. It differs structurally from other linear lantibiotics including nisins A and Z. ¹³⁰ , ¹³¹ Class II enterocins are two‐peptide bacteriocins of the pediocin family. ¹³² The most common antimicrobial peptides are pediocin‐like enterocins, also known as Class II‐1 bacteriocins, which are classified into two subgroups based on sequence similarity. ¹³³ All of them have a conserved YGNGVXC “pediocin box” motif and a β‐sheet domain supported by a conserved disulfide bridge at the N‐terminus. ¹³⁴ Enterocin A, mundticins, and enterocin CRL5 are among the first subgroup. ¹²⁹ The second subgroup is represented by bacteriocin 31, bacteriocin T8, bacteriocin RC714, enterocin SEK4, enterocin P, and enterocin M. ¹²⁹ Class II‐2 bacteriocins lack the YGNGVXC motif and are not synthesized with a leader peptide; however, they must have complementary actions of both peptides to be completely active. ¹³ A main subgroup includes enterocin Q, enterocin C, two‐peptide bacteriocin L50 (A, B), enterocin RJ‐11, and enterocin EJ97.8. Other linear non‐pediocin‐like enterocins with a leader peptide are classified as Class II‐3. The presence of a second peptide may reinforce their antimicrobial activity. Class III enterocins are cyclic peptides including enterocin AS‐48 produced by E. faecalis S‐48. Finally; Class IV includes a large and heat‐labile bacteriocin, named enterolysin A produced by E. faecalis. Enterocins have a wide range of antimicrobial activity, inhibiting not only the growth of closely associated bacteria but also Gram‐positive pathogens such as L. monocytogenes, S. aureus, and V. cholerae in food. This particularity has been observed for example in enterocin LD3, enterocin CV7, enterocin B, enterocin Gr17, enterocins A and B, and enterocin dP. ¹²⁹ Besides, these bacteriocins show broad‐spectrum antimicrobial activity against Gram‐negative bacteria such as E. coli, Salmonella sp., Psudomonas spp., and Vibrio sp. ¹³⁵ , ¹³⁶ , ¹³⁷ , ¹³⁸ Also, they are considered as one of the weapons against multidrug‐resistant pathogens and prevent biofilm formation. The main multidrug‐resistant organisms include ESBL‐producing Enterobacteriaceae, MRSA, and VRE. ⁶⁰ , ¹³⁹ Despite their potent activity against foodborne pathogens, enterococcal bacteriocins have not yet been approved for use in natural food preservation due to safety concerns. ¹²⁶ Recently, E. faecium SF68^® (NCIMB 10415, Cerbios‐Pharma SA, Barbengo, Switzerland) and E. faecalis Symbioflor 1 (SymbioPharm, Herborn, Germany) are commercially available on the market as two probiotic strains. ¹²⁹ , ¹⁴⁰

TABLE 2.

Bacteriocins of Enterococcus and their main characteristics

Bacteriocin	Production strain	Source	Molecular mass	Heat‐stability range	PH‐Stability range	Stability	Sensitivity	Production parameter	Inhibitory‐activity spectrum	Reference
Enterocin LD3	E. hirae LD3	Dosa	4.1	At 121°C for 30 min	2–6	Amylase lipase	Papain Proteinase K Pepsin Trypsin	MRS	S. aureus P. fluorescens P. aeruginosa S. typhi S. flexneri L. monocytogenes E. coli O157:H7 E. coli (urogenic, a clinical isolate) Vibrio sp.	(135, 136)
Unnamed	E.mundtii QAUEM2808	Fermented milk product Dahi	(−)	(−)	(−)	(−)	(−)	TSB	E. coli ATCC 10536 S. aureus ATCC 6538 P. aeruginosa ATCC 9027 L. monocytogenes ATCC 13932	138
Enterocin B	E.faecium YT52	Boza	5.5	At 100°C for 20 min	5.0–10.0	Lipase Lysozyme Catalase	Proteinase K Trypsin a‐chymotrypsin Pepsin	GM17 (10 h) logarithmic growth phase (7 h)	L. monocytogenes B. cereus	141
Nisin	E. hirae DF105Mi	Goat milk	(−)	At 121°C for 20 min	2.0–12.0	Detergents α‐amylase Catalase	Proteinase K Pronase Trypsin Pepsin Papain	MRS, exponential phase	L. monocytogenes	142
Faerocin MK	E.faecium M3K31	Vigna mungo	N.D	At 100 °C for 30 min	2–12	NaCL	Proteinase K Papain	MRS (18 h)	L. monocytogenes S. aureus E. coli E. herbicola B. subtilis B. cereus P. aeruginosa	143
TJUQ1	E.faecium	Pickled Chinese	(−)	4–45°C	6–9	(−)	(−)	MRS Overnight under static condition	L. monocytogenes CMCC 1595	144
KT11”	E. faecalis KT11	Cheese	~3.5	At 121°C for 30 min	2–11	Surfactants Solvents	Proteinase K α‐chymotrypsin Protease Trypsin	MRS (24 h)	Vancomycin‐ and/or methicillin‐resistant bacteria L. monocytogenes S. aureus ATCC25923 B. subtilis S. aeruginosa, K. pneumoniae, S. marcescens E. aerogenes	60
Enterocin CV7	E. faecalis CV7	Chicken	4.5	At 121°C for 10 min	2–12	Solvents Detergents	Pepsin Proteinase K Trypsin Chymotrypsin Catalase Lipase	MRS (24 h)	Gram‐positive bacteria: L. monocytogenes S. aureus Gram‐negative bacteria: Salmonella sp. S. thypi S. enterica E. coli V. fischeri	137
EF478	E. faecalis	Water	45	2–8	At 60°C for 1 h, at 4°C for 6 months, at 25°C for 2 months, and at −20°C for one year	Amylase Lipase	Proteinase K Trypsin α‐chymotrypsin	MRS (16 h) PH: 5–6	E. faecalis ATCC 51299 E. faecium ATCC 35667	145
Enterocin dP	E. lactis Q1	Shrimp	(−)	4.0–9.0	At 100°C for 15 min	(−)	Proteinase K Trypsin	MRS Aerobic conditions	L. monocytogenes P. aeruginosa L. garvieae Fungi (Aspergillus niger and Fusarium equiseti)	146
B3A‐B3B	E. faecalis B3A‐B3B	Feces	5.2	2–10	(−)	CFS	Proteinase K Trypsin Papain Lipase Catalase Lysozyme	MRS (24 h)	L. monocytogenes S. aureus Methicillin‐resistant S. aureus (MRSA) C. perfringens	139
152A and L50B	E. durans 152	Floor	5	2–8	At 121 ℃ for 15 min	(−)	Proteinase K	TSB (24 h)	L. monocytogenes	147
DU10	E.faecalis DU10	Duck intestine	6.3	2–12	At 121°C for 10 min	Detergents Solvents	Proteinase K Pepsin Trypsin α‐chymotrypsin	MRS	Gram‐positive bacteria: L. monocytogenes S. aureus Gram‐negative bacteria: S. typhi S. enterica Salmonella sp. E.coli	148
Enterocin A, B	E.faecium GGN7	Cow milk	4.8 and 5.4	2–8	At 121°C for 10 min	(−)	Proteinase K Trypsin	MRS (16 h)	L. ivanovii BUG 496 P. aeruginosa 27853	149
F4‐9	E.faecalis F4‐9	Red fish	5.5	2 – 6	At 100°C for 15 min	(−)	Trypsin Chymotrypsin Proteinase K	MRS (16 h)	A Gram‐negative strain Enterococcus B. coagulans E. coli JM109	150
CRL 1826	E. gallinarm CRL 1826	Captive bullfrog	(−)	2–9	At 80°C for 30	Solvents Lipase α‐amylase	a‐chymotrypsin Trypsin Pepsin	MRS Microaerophilic conditions	Citrobacter freundii P. aeruginosa (bullfrog pathogens) L. monocytogenes	151
LD3	E. hirae strain LD3	Dosa batter	Between 3.48 and 7.68	2 – 6	At 121°C for 15 min	Solvents Detergents Catalase Amylase Lipase	Pepsin Trypsin Proteinase K Papain	MRS (18 h)	S. aureus P. fluorescens P. aeruginosa, S. typhi S. flexneri L. monocytogenes E. coli O157:H7 Vibrio sp.	152
SH01	E.faecium SH01	Mukeunji	3	2–12	At 121°C for 15 min	α‐Amylase Catalase Detergents	α‐chymotrypsin Pronase E Proteinase K Trypsin	MRS Early stationary (24 h)	L. monocytogenes KCTC 3569 L. curvatus KFRI 166 L. mesenteroides ATCC 10830 (agar‐well‐diffusion assay)	153
FL31	E.faecium	(−)	3.5	2–9	At 100°C for 90 min	Surfactants Solvents	Trypsin Pronase E Proteinase K	MRS Early stationary	L. monocytogenes ATCC19117	154

11.1.3. Bacteriocins of Streptococcus

The genus Streptococcus embraces a broad range of Gram‐positive bacteria, some of which are pathogenic species, while others are important for use in dairy products fermentation. S. thermophilus is the only streptococcal species that along with Lactobacillus spp. is used as an industrial dairy starter culture, especially for yogurt manufacturing. ¹⁵⁵ It could improve the quality of fermented dairy products through various probiotic effects and the production of bacteriocins, flavor substances, and extracellular polysaccharides. ¹⁵⁶ Renye et al. ¹⁵⁷ demonstrated that S. thermophilus strain ST109 produced an antimicrobial peptide against lactobacilli, enterococci, and human pathogen S. pyogenes. Various studies have reported the ability of Streptococcus spp. against human pathogens and common foodborne bacterial pathogens ¹⁵⁸ , ¹⁵⁹ , ¹⁶⁰ (Table 3). In another study by O'Connor et al., ¹⁶¹ S. hyointestinalis DPC6484 isolated from the porcine intestine was shown to produce a bacteriocin designated as nisin H with a molecular mass of 3,453 Da, exhibiting an antimicrobial activity against a wide range of Gram‐positive genera. The use of nisin variants as natural food preservatives has been reported in over 50 countries worldwide without inducing microbial resistance. ¹⁶²

TABLE 3.

Bacteriocins of Streptococcus and their main characteristics

Bacteriocin	Production strain	Source	Molecular mass	Stability	Sensitivity	Production parameter	Inhibitory spectrum	Reference
Nisin H	S. hyointestinalis DPC6484	Porcine intestine	3.4	(−)	(−)	TSB at 37°C	E. coli DPC6912 B. cereus 9139 L. delbrueckii subsp. bulgaricus LMG6901 L. lactis subsp. cremoris HP E. faecalis 6307 S. agalactiae ATCC 13813 S. agalactiae DPC5338 S. bovis DPC6491 S. gallolyticus DPC6501 L. innocua DPC3572 L. monocytogenes 1042 S. aureus ATCC 25923 S. aureus DPC5245 S. hyointestinalis DPC6484 S. uberis strain 42	161
Unknown	Streptococcus species (G3, G4)	Green gram	(−)	PH: 5	(−)	MRS broth at 37°C for 48 h	P. aeruginosa S. aureus E. coli Klebsiella	160
Thermophilin 109	S. thermophilus ST109	Raw milk	5–6	At 121°C for 17 min.	B. subtilis protease Proteinase K Trypsin a‐amylase	TYL broth for 18 h	In TYL broth: Other S. thermophilus strains L. delbreuckii ssp. bulgaricus L. acidophilus S. pyogenes In M17G broth: E. faecalis E. faecium	157
Suicin 65	S. suis 65	Pigs	3.3 (SDS‐PAGE)	Enzyme: trypsin, chymotrypsin, proteinase K/30 min PH: 2 and 11 Heat: 121°C for 15 min	(−)	Todd Hewitt agar (THA) plates supplemented with 0.01% Tween 80	S. suis strains from different countries	158
Suicin 3908	S. suis serotype 2	Pigs	3.3 (SDS‐PAGE)	Enzymes: trypsin, chymotrypsin, proteinase PH: 2 and 11 Heat: 121°C for 15 min	(−)	2 L of a culture medium containing 2% proteose‐peptone, 1% yeast extract, 0.25% glucose, 0.25% NaCl, 0.3% K2HPO4, 0.2% KH2PO4, 0.01% MgSO4 · 7 H2O, and 0.002% MnSO4 · 7 H2O (pH 7.0)	S. hyicus	159

11.1.4. Bacteriocins of Pediococcus

Pediococcus is a type of lactic acid bacteria, which plays a major function in the preservation of fermented food products such as vegetables, meat, sausage products, and cheddar cheese. ¹⁶³ Bacteriocins of Pediococcus species are designated as pediocins and produced by three species that play an important role in food biopreservation, including P. acidilactici, P. cerevisiae, and P. pentosaceus. They generally belong to the Class IIa bacteriocin family with a small molecular weight (<5 kDa); the identified N‐terminal region of all pediocins includes a pattern known as "pediocin box." They show a wide range of antimicrobial activity against other bacteria related to food spoiling and health jeopardies of food source. The biological and chemical characteristics of pediocins are shown in Table 4. Various species are stable in a broad span of pH and temperature, which makes them suitable for biopreservation of various food products. ¹⁶⁴ Production of bacteriocin usually occurs during the stationary growth phase in MRS broth. Several studies have reported that both P. acidilactici and P. pentosaceus are associated with food fermentation and produce various pediocins which inhibit several food spoilage and human pathogenic bacteria. ³² Pediocins are Class IIa bacteriocins produced by Pediococcus spp., which are commercially accessible under the name Alta 2341TM or Microgard TM. These bacteriocins are more effective than nisin against certain foodborne pathogens, such as L. monocytogenes and S. aureus, and Gram‐negative organisms such as Pseudomonas and E. coli. The potential application of pediocins in dairy products is further enhanced by considering their stability in aqueous solutions over a wide pH range and in heating or freezing systems. Despite this high possibility, a few studies have examined the addition of pediocins to milk or dairy products. Pediocin PA1 was found to reduce L. monocytogenes numbers in cottage cheese, cream, and cheese sauce by Garsa et al. ¹⁶⁵

TABLE 4.

Bacteriocins of Pediococcus and their main characteristics

Bacteriocin	Species	Source	Mol. wt. (kDa)	Heat stability range	Sensitivity	PH Stability range	Production phase	Optimal Production	Inhibitory activity spectrum	Reference
VJ13B	P. pentosaceus VJ13	Idli batter	4.0	At 100°C for 1 h	Protease	2–8	MRS broth (24 h)	Heat: 37°C PH: 5.0–6.0	M. smegmatis K. pneumonia L.monocytogenes C. perfringens S. epidermidis	172
NKSM1	P. pentosaceus NKSM1	Appam batter	9–14	At 110°C for 2 h	Trypsin Papain	4–7.5	MRS broth (48 h)	Heat: 30°C PH: 6.0	L. monocytogenes MTCC 657 A. baumannii MTCC 1425	173
A11 and C12	P. acidilactici A11 and C12	Breast milk isolate (ASI)	(−)	(−)	(−)	(−)	MRS broth (24 h)	Heat: 37°C	MRSA	174
BLIS	P. pentosaceus ATCC 43200	Shake flasks to bioreactor	75	At 121°C for 15 min	(−)	3.8–6.5	MRS broth (16 h)	Heat: 37°C PH: 6.0 ± 0.2 Addition of 1.0 N HCl	L. innocua L. seeligeri	41
Pediocin L50	P. acidilatici FS6	Human breast milk	2.7–17	(−)	(−)	2.5	MRS broth (24 h)	Heat: 37°C PH: 2.5	E. coli 0157:H7 L. monocytogenes ATCC 15313 B. cereus ATCC 14576 S aureus ATCC 19095 H. pylori	175
PE‐ZYB1	P. pentosaceus zy‐B	Intestine of Mimachlamys nobilis	2.02	At 121°C for 20 min	Trypsin	2–10	MRS broth (48 h)	Heat: 37°C PH: 2–7	L.monocytogenes	49
(−)	P. pentosaceus	Brazilian artisanal cheese	(−)	At 121°C for 15 min	Proteinase K Trypsin Pepsin α‐Chymotrypsin Protease type XIV	2–10	MRS broth (24 h)	Heat: 37°C PH: 6.5	L. monocytogenes 211 L. monocytogenes 422	51
(−)	Pediococcus acidilactici K10	Kimchi	(−)	(−)	(−)	2.5–4	MRS broth (24 h)	Heat: 37°C PH: 3.0	S. typhimurium E. coli O157:H7	176
Pediocin	P. acidilactici CFR K7	Pickles and dry‐cured meats	5	At 121°C for 20 min	Pepsin Trypsin Proteinase K	2–11	MRS broth (48 h)	Heat: 30°C PH: 6.0	S. aureus E. coli	177
	P. acidilactici	Gappal			Protease Pepsin Trypsin		MRS broth (12 h)	Heat: 30°C PH: 6.0	E. faecalis ATCC 19433 M. luteus ATCC 49732 S. aureus ATCC 2523 L. monocytogenes B. megaterium B. sphaericus B. cereus

In a study, pediocin PA‐1 was derived from P. acidilactici PAC1 and shown to lyse a strain of L. monocytogenes. ¹⁶⁶ Choi and Beuchat ¹⁶⁷ isolated a bacteriocin from P. acidilactici, which had a deadly result on L. monocytogenes. Jamuna and Jeevaratnam ¹⁶⁸ extracted a bacteriocin from P. cerevisae P18, which was composed of a combination of proteinaceous materials and was active against L. monocytogenes. Pediocin A was obtained in a study from P. pentosaceus with a molecular mass of 80 kDa, which had inhibitory activity against Lactobacillus, Leuconostoc, Pediococcus, Staphylococcus, Enterococcus, Listeria, and Clostridium species. ¹⁶⁹ A new bacteriocin was obtained in a study from P. pentosaceus ACCEL with a molecular mass of 17.5 kDa and stability at pH 2.0–6.0; only Gram‐positive bacteria were inhibited by this bacteriocin. ¹⁶⁵ A new proteinaceous compound with a molecular mass of 23 kDa has been derived from P. pentosaceus for the first time, which is active against S. dysenteriae; this bacteriocin could be supplemented into any food to make it safe against S. dysenteriae as a foodborne pathogen causing alarm in many developing countries. ¹⁷⁰ A pediocin‐producing strain of P. acidilactici able to survive in the GI tract has been recently isolated and found to be an effectual inhibitor of various Gram‐positive bacterial pathogens, such as Enterococcus spp. and L. monocytogenes. It demos inhibitory activity against gastric adhesion of opportunistic pathogens, such as Klebsiella, Pseudomonas, and Shigella species. ¹⁷¹ Speelmans et al. (2006) isolated P. pentosaceus 05–10 from a traditionally fermented Sichuan pickle, which could produce a bacteriocin designated as pediocin 05–10 active against Listeria, Lactobacillus, Streptococcus, Enterococcus, Pediococcus, and Leuconostoc. The broad anti‐Listeria activity exhibited by pediocin 05–10 is the characteristic of Class IIa bacteriocins. Pediocin 05–10 was sensitive to proteolytic enzymes but stable at pH 2–10 and resistant to heat (15 min at 121°C). ¹⁷¹

11.1.5. Bacteriocins of Carnobacterium

Carnobacterium spp. isolated from poultry, fish, and vacuum‐packaged meat were initially accepted as non‐aciduric lactobacilli by Parada et al. ¹⁷⁸ The carnobacterial bacteriocins belong to the Class I and II bacteriocins. ¹⁷⁹ Many studies have reported bacteriocins associated with this genus, which inhibit the growth of spoilage microorganisms in foodstuffs. ¹⁸⁰ , ¹⁸¹ MMF‐32 and KOPRI 25789 are produced by C. maltaromaticum KOPRI 25789 and C. maltaromaticum MMF‐32 and show antimicrobial activity against L. monocytogenes and Gram‐negative bacteria in smoked salemon. High bacteriocin production occurs at 30°C and optimal pH 5–7. Additional experiments have indicated that producer isolates effectively inhibit foodborne pathogens in vitro, presumably due to the effects of bacteriocins. ¹⁸² , ¹⁸³ Their resistance and/or sensitivity to proteases, general pH, and heat confirm the presence of bacteriocins and their potential usage as biopreservatives in food products (Table 5).

TABLE 5.

Bacteriocins of Carnobacter and their main characteristics

Bacteriocin	Species and strain	Source	Mol. wt. (kDa)	Heat stability range	Sensitivity	PH Stability range	Production phase	Optimal production	Inhibitory activity spectrum	Reference
MMF−32 and KOPRI 25789	C. maltaromaticum MMF−32 C. maltaromaticum KOPRI 25789	Smoked salmon	—	At 56°C for 30 min and at 100°C for 10 min	Lysozyme Proteinase K Trypsin α‐Chymotrypsin	3.5–6.5	MRS broth (48 h)	Heat: 30°C, PH: 6.5±0.2	Shewanella baltica OS185 L. monocytogenes ATCC 19114 Aeromonas HB−6 A. hydrophila HX201006‐3 S. baltica S. baltica OS678 Serratia I−113–31 A. salmonicida subsp. achromogenes	184
‐	Chromobacterium aquaticum	Zebrafish	—	At 100°C for 20 min	Protease Xylanase	2–11	TSB agar (30 h)	Heat: 30°C PH: 5–7	A. hydrophila S. iniae	182
Piscicolin 126, carnobacteriocin BM1, and carnocyclin A	C. maltaromaticum	Lean beef	—	At 100°C for 20 min		2–11	LB broth (48 h)	Heat: 30°C PH: 5.4	E. coli AW1.7 S. enterica Typhimurium	183

11.1.6. Bacteriocins of Leuconostoc

Leuconostoc spp. are lactic acid bacteria that are most commonly associated with fermented food products, such as fermented sausages, fermented vegetables, cereal products, and a wide variety of fermented milk products. ¹⁸⁵ , ¹⁸⁶ They are environmental organisms that are generally found in fresh plants, raw milk, or chilled food products. ¹⁸⁵ Leuconostoc spp. have the ability to produce aroma compounds (diacetyl and acetoin) in dairy products by metabolizing citrate. ¹⁸⁷ Antimicrobial activity of these organisms has long been recognized. ¹⁸⁸ Several studies have identified bacteriocin‐producing strains of leuconostocs (Table 6). ¹⁸⁹ , ¹⁹⁰ , ¹⁹¹ Most Leuconostoc bacteriocins are classified as Class II, which are small (less than 10) and heat stable. They are non‐lanthionine‐containing bacteriocins without post‐translational modification. ¹⁶ Several strains of Leuconostoc spp. could produce bacteriocin (Table 6). According to Table 6, L. mesenteroides is the most common bacteriocin‐producing species. They mainly prevent the growth of Gram‐negative and Gram‐positive bacteria, including E. coli, Salmonella, Listeria spp, and S. aureus, which are foodborne pathogens. Therefore, this species is considered as a good candidate for the use in fermented food products in the food industry.

TABLE 6.

Bacteriocins of Leuconostoc and their main characteristics

Bacteriocin	Production strain	Source	Mol. wt. (kDa)	Heat‐stability range	Stability	pH Stability range	Sensitivity	Production parameter	Inhibitory activity spectrum	Reference
BacCHBY46	L. mesenteroides CHBY 46	Algerian dromedary milk	3.5 (Tricine‐SDS‐PAGE)	80–100°C	(−)	PH: 2–6	Protease α‐chymotrypsine Trypsine	MRS broth	S. aureus ATCC 29213 P. aeruginosa L. innocua ATCC 33090 E. coli ATCC 25922 S. aureus ATCC 29213 K. oxytoca ATCC 13182 E. cloacae ATCC 13047 E. faecalis ATCC 10541 B. cereus ATCC 10876 P. aeruginosa ATCC 27653	192
Unknown	Leuconostoc spp.	Stored meat	(−)	(−)	(−)	(−)	(−)	MRS broth	E. coli S. typhimurium S. aureus L. monocytogenes	193
L. lactis SD501	L. lactis SD501	Kimchi	7	At 121 ℃ for 15 min	Catalase Amylase Lipase Pepsin	1–10	Proteinase K α‐chymotrypsin	Early stationary phase in MRS broth at 37°C	L. monocytogenes E. faecalis	190
Unknown	L. pseudomesenteroides	Tibetan yaks	(−)	(−)	(−)	(−)	(−)	MRS broth for 24	E. coli S. aureus S. enteritidis S. aureus	194
Unknown	L. lactis BT17	Boza	(−)	(−)	(−)	(−)	(−)	MRS broth	E. coli ATCC 25922 Salmonella sp. K. pneumoniae	195
Leucocin K7	L. mesenteroides	Pickles	(−)	0–100°C	(−)	2–10	Pepsin Protease K Papain	MRS at 30°C for 24 h	L. monocytogenes strains CMCC54005 S. aureus ATCC 29213 P. aeruginosa ATCC 27653	196
BLIS 213M0	L. mesenteroides subsp. dextranicum	Mongolian fermented mare milk and airag	2.6–3. (SDS‐PAGE)	25°C for 1 week 121°C for 15 min	(−)	2 −11 4.5	Pepsin Trypsin α‐Chymotrypsin Proteinase K	MRS broth at 25°C exponential growth phase of the producer cells	Listeria spp. E. faecalis L. mesenteroides P. pentosaceus S. thermophilus	189
Unknown	L. mesentroides	Domestic goat	(−)	(−)	(−)	4.2–9.2	(−)	MRS broth at 35°C for 24 h PH: 6.2	S.aureus ATCC25923 E.coli ATCC25422 P.aeruginosa ATCC27583 K.pneumonia ATCC700603	191
Mesentericin W3	L. mesenteroides subsp. cremoris	Wine	3.9 (MALDI‐TOF MS)	(−)	Acetonitril 2‐propanol Methanol Acetone Chloroform Ethanol	2 and 7	Proteinase K Trypsin	MRS broth pH 6.5 at 30°C	Lactobacillus Leuconostoc Carnobacterium Listeria Enterococcus	197
Unknown	L. mesenteroides strain P45	Pulque, a Mexican traditional alcoholic beverage	(−)	(−)	Lysozyme Bile salts	3.5	(−)	MRS or APT (DIFCO) broth at 30°C	L. monocytogenes Enteropathogenic E. coli S. enterica serovar Typhi S. enterica serovar Typhimurium	198
Unknown	L. mesenteroides Com−54	Kimchi	(−)	(−)	(−)	(−)	Trypsin Lysozyme	MRS broth	Salmonella	199
Homology with mesentericin Y105 (peak 1) and mesentericin B105	L. mesenteroides subsp. mesenteroides SJRP55 strain	Water Buffalo Mozzarella cheese	3.9 and 3.4 (Mass Spectrometry (MS))	At 100°C for 2 h 121°C for 20 min	Enzymes: α‐amylase Lipase Catalase Solvents: SDS Tween 20 Tween 80 Triton X−100 Na‐EDTA NaCl (1%) 1 M urea	2–4	Pepsin Protease Trypsin α‐chymotrypsin	MRS broth at 25°C Late log phase until the stationary phase	Listeria spp.	200
Unknown	L. mesenteroides subsp. mesenteroides L. mesenteroides subsp. Dextranicum	Traditional date product "Btana"	(−)	At 55°C for 15 min	(−)	4.8–6.5	(−)	MRS broth	P. aeruginosa ATCC 27853 E. faecalis ATCC 29212 E. coli ATCC 25922 S. aureus ATCC 25923	201

11.1.7. Bacteriocin of Bifidobacterium

Intestinal microbial balance could be improved by suppressing the growth of different potentially pathogenic microorganisms. The production of organic acids and the secretion of antimicrobial compounds such as bacteriocins may be induced by antimicrobial activity of bifidobacteria. ²⁰² Purified bifidocin A shows a wide span of antimicrobial activity against a great deal of food spoiling pathogenic bacteria such as E. coli, L. monocytogenes, S. aureus, and some yeasts ⁵³ (Table 7). Bifidocin A is produced in the exponential growth phase with the maximal production in the midi‐stationary phase. This suggests that bifidocin A production depends on the cell number, and bifidocin A is a secondary metabolite. ²⁰³ The reduction in the activity of bifidocin A at the end of the stationary phase may be because of the activity of endogenous extracellular proteases, which peak pending this growth phase. ²⁰⁴ A sensitive strain (E. coli 1.90) was tested in a study to determine whether bifidocin A has a bactericidal or bacteriostatic mode of action. The outcome displayed that the inhibitory activity of bifidocin A against E. coli 1.90 was bactericidal with cell lysis, which is consistent with that of bifidocin B. ²⁰⁵ Antimicrobial activity of substances made by several Bifidobacterium strains (B. bifidum and B. lactis Bb‐12) is curbed to Gram‐negative pathogenic bacteria. ²⁰⁶ Yildirim et al. (1999) showed that their application could be beneficial in the food commercial enterprise in modelling HACCP plans to effectively delete Gram‐negative pathogenic bacteria in meat products, especially E. coli 0157:H7 xx. Bifidocin B was made in a study in the exponential growth phase and reached a peak activity of 3,200 AU/mL at the primary stationary phase. Bifidocin B had a molecular mass of 3.3 kDa as analyzed by tricine‐sodium dodecyl sulfate‐polyacrylamide gel electrophoresis. ²⁰⁷ , ²⁰⁸

TABLE 7.

Bacteriocins of Bifidobacterium and their main characteristics

Bacteriocin	Species and strain	Source	Mol. wt. (kDa)	Heat stability range	Sensitivity	PH Stability range	Production phase	Optimal production	Inhibitory activity spectrum	Reference
BB04 bifidocin A	B.animals	Healthy centenarians feces	1.9	At 100°C for 30 min	Trypsin Pepsin Proteinase K Acid proteinase Neutral proteinase	2–11	MRS broth 32	Heat: 37°C PH: 8.0	E. coli L. monocytogenes S. aureus	53
Bifidin or bifilact Bb−12	Bifidobacterium bifidum and B. lactis Bb−12	Cow meat (round cuts) and fat	—	At 121°C for 15 min	—	4–10	MRS broth 16	Heat:37°C PH: 5–7	A. hydrophilia A. caviae A. sobria P. flouresent P. aeruginosa P. fragi E. coli 0157:H7.	206
Bifidin I	B.animalis subspLactis	Cheese Whey	—	—	Proteolytic enzymes	6	MRS broth (48 h)	Heat:37°C PH: 6.0	L. monocytogenes ATCC 13932 E. coli ATCC 25922 L. sakei ATCC 15521	209
Bifidoadocin	B. adolescentis	Saliva of 18 volunteers postmenopausal women	14.6	At 121°C for 15 min	Pepsin Lipase α‐amylase Papain Chymotrypsin	2–10	MRS broth (24 h)	Heat:37°C PH: 6.0	E. coli American Type Culture Collection (ATCC) S. aureus ATCC	210
Bifidin I	B. infantis BCRC 14602	—	3	At 121°C for 15 min	—	4–10	MRS broth (18 h)	Heat:37°C PH: 5–7	LAB strains Staphylococcus Bacillus Streptococcus Salmonella Shigella E. coli	203

11.1.8. Bacteriocins of Lactococcus

Nisin is categorized as a Class‐Ia bacteriocin or lantibiotic. To date, eight types of nisin have been observed and characterized. Nisins A, Z, F, and Q are produced by L. lactis, and nisins U, U2, P, and H are made by some Streptococcus strains. ²¹¹ , ²¹² Nisins effectively belong to the Class I bacteriocins that contain lanthionine and have a double mode of action: (i) they attach to lipid II which is the chief transporter of peptidoglycan subunits from the cytoplasm to the cell wall, inhibit precise cell wall synthesis, and induce cell death, and (ii) they take lipid II as a docking molecule to start the process of membrane insertion and pore formation, leading to speedy cell death. ²¹² Nisin shows antimicrobial activity against some Gram‐positive bacteria, including LAB, pathogens such as Listeria and Staphylococcus, and spore‐forming bacteria such as Bacillus and Clostridium (Table 8). Nisin has been used extensively in cheese and pasteurized cheese spreads as an alternative to nitrate in order to hinder the outgrowth of clostridia spores. ²¹¹ Some research has been undertaken to show the efficacy of nisin (or other bacteriocins) against L. monocytogenes in fresh products. Some studies have focused on combination treatments, for example, nisin in combination with acids and EDTA. ²¹³ The combined effect of nisin and bovicin HC5 against L. monocytogenes and S. aureus in fresh cheese was investigated by Pimentel‐Filho et al. (2014). They reported a significant diminution in L. monocytogenes count to an undiscernible level after 9 days of storage at 4°C; however, the combined effect of bacteriocins did not stop the growth of S. aureus. ²¹⁴ Józefiak et al. ²¹⁵  made use of a nisin‐supplemented bird diet to feed broiler chickens and found a decrease in the amount of Bacteroides and Enterobacteriaceae in ileal digesta of chickens fed by nisin‐supplemented diet. Nisin A and lacticin Q produced by L. lactis are more effective in reducing planktonic cells than methicillin‐resistant S. aureus biofilm cells. ²¹⁶ In addition to LAB bacteriocins, a non‐LAB bacteriocin, named sonorensin, was purified by Chopra et al. ²¹⁷ from B. sonorensis and displayed a significant anti‐biofilm activity against S. aureus. To date, only nisin (Nisaplin, Danisco) and pediocin PA1 (MicrogardTM, ALTA 2431, Quest) have been commercialized as food compounds. ²¹⁸ However, some other LAB bacteriocins propose promising outlook for use as biopreservatives, such as enterocin AS‐48 ²¹⁹ or lacticin 3147 ²²⁰ ; no other bacteriocin has been proposed for industrial application. Lacticins are made by specific strains of L. lactis and include lacticin 3147 and lacticin 481. Lacticin 3147 powder was analyzed by Morgan et al. ²²¹ and found to be effective in controlling Listeria and Bacillus in infant milk formulation, natural yoghurt, and cottage cheese. Lacticin 481 is a single‐peptide lantibiotic with a moderate spectrum of inhibitory activity, which is primarily active against other LAB, C. tyrobutyricum, and L. monocytogenes. The utilization of semi‐purified lacticin 481 in fresh cheese stored at refrigeration temperatures was investigated by Ribeiro et al. (2016), leading to a 3‐log reduction in L. monocytogenes amount during 3–7 days. However, the use of lacticins in food products is unlikely to ensure full deletion of pathogens such as L. monocytogenes. ²²² Lactococcin BZ is made by some strains of L. lactis spp. (lactis BZ) and shows broad antibacterial activity against Gram‐positive and Gram‐negative bacteria. This bacteriocin also demonstrations powerful antilisterial activity in milk. Partially purified lactococcin BZ (400–2500 AU/ml) was demonstrated in a review to decrease L. monocytogenes count to an undetectable level in both skim and full‐fat milk during the storage at 4 and 20°C. In addition, this antilisterial activity was stable until the end of the storage period ²⁵ and was not adversely influenced by the milk fat content. ²²³

TABLE 8.

Bacteriocins of Lactococcus and their characteristics

Bacteriocin	Species and strain	Source	Mol. wt. (kDa)	Heat Stability range	Sensitivity	PH Stability range	Production phase	Optimal production	Inhibitory activity spectrum	Reference
BacL49	L. lactis	Moribund sleepy cod	5 and 54	At 100°C for 1 h	Proteinase K α‐chymotrypsin Trypsin Papain	2.5–9.5	Heart infusion broth (BHI) or agar (10–12 h)	Heat: 28°C PH: 5.5	S. iniae	224
LABW4	L. lactis	Naturally fermented milk	—	—	Proteinase K	5–7	MRS broth (24 h)	Heat:37°C PH: 6.5	L. monocytogenes MTCC657V	225
A5	L. lactis A5	Gastro‐intestinal tissues of Broadhead catfish	3.4	At 121°C for 15 min	Proteinase K	—	MRS broth (18 h)	Heat: 37°C	B. cereus S. aureus S. thyphimurium	226
Gt28, Gt29, and Ella8	L. lactis	Native fruits of Ecuador subtropical rainforest	—	At 121°C for 15 min	Proteinase K Pepsin Lysozyme α‐chymotrypsin	2–10	MRS broth (20 h)	Heat: 37°C PH: 6.0	S. enterica ATCC 51741 E. coli ATCC 25922	227
CJNU 3001	L. lactis	Kimchi	—	At 100°C for 15 min	Protease		MRS or RCM broth (24 h)	Heat: 25, 30, and 37°C	S. aureus KCTC 3881	228
Nisin Z‐producing	lactis subsp. lactis KT2W2L	Brackish water from a mangrove forest	—	At 100°C for 10 min	—	7	M17 medium (24 h)	Heat: 25°C PH: 7.0	Brochothrix thermosphacta DSMZ 20171T S. aureus CIP 76.25	229
Nisin Z	L. lactis	Freshwater fish	4.10	At 80°C for 15 min	Catalase Trypsin α‐Amylase Lipase	2–10	MRS broth (15 h)	Heat: 30°C PH: 6.5	L. plantarum 5S E. faecalis ATCC 51299 S. aureus ATCC 25923	230
BGBU1‐4	L. lactis	Cheese making	—	—		—	MRS broth (48 h)	Heat: 37°C	L.monocytogenes ATCC19111 S. aureus LMM322	231
Ent35‐MccV	L. lactis NZ9000	Milk	1.5–15	At 100°C for 10 min	Protease	7	M17 broth (16 h)	Heat: 30°C PH: 6.5	L. monocytogenes E. coli	232
LABW4	L. lactis	Home‐made buttermilk	‐	At 121°C for 15 min	Trypsin Papain Proteinase K Lysozyme	3–11	MRS broth (48 h)	Heat: 28°C PH: 5–7	S. aureus MTCC96 P.aeruginosa MTCC741	233
DF4Mi	L. lactis	Goat milk	‐	At 100°C for 2 h, and at 121°C for 20 min	Proteinase K Protease Pepsin α‐chymotrypsin	2–10	MRS broth (48 h)	Heat: 30°C PH: 5–7	L. monocytogenes ATCC 7644	234

11.2. Bacteriocins of Gram‐negative bacteria

Bacteriocins of Gram‐negative bacteria could be classified into three groups: peptide bacteriocins, colicin‐like bacteriocins (CLBs), and tailocins. Recent studies on E. coli, S. enterica, Hafnia alvei, C. freundii, K. oxytoca, K. pneumoniae, and E. cloacae have revealed that bacteriocin production level varies from 3% to 26% among environmental isolates.

11.2.1. Colicin

Colicins produced by E. coli are present in 30–50% of strains isolated from human hosts. E. coli colicins have been the most widely studied Gram‐negative bacteriocins since their discovery; they are now used as a model system for studying bacteriocin structure/function, genetic organization, ecology, and evolution. ²³⁵ Nomura and Witten ²³⁶  showed that colicins E1 and K inhibited macromolecular synthesis without arrest of respiration, colicin E2 triggered DNA breakdown, and colicin E3 inhibited protein synthesis. According to recent evidence, the frequency of bacteriocin production in E. coli populations could vary from 10 to 80%, depending on the animal host from which they are isolated, the diet of the host, temporal changes, and the type of bacteriocin produced by the strain. When colicins enter the target cell, they could be divided into three categories based on their bactericidal mechanisms as follows: (i) pore‐forming colicins, including colicins A, B, E1, Ia, Ib, K, and N, are those colicins that act through the formation of pores or channels in the inner‐membrane to cause leakage of cytoplasmic compounds, destruction of electrochemical gradient, ion loss, and cell death; (ii) nuclease colicins, including colicins E2 to E9, are those colicins that contain DNase, 16S rRNase, and tRNase and act non‐specifically to digest cellular DNA and RNA of target bacteria; and (ii) peptidoglycanase colicins are proteins that could digest the peptidoglycan precursor, preventing the synthesis of peptidoglycan by bacteria and ultimately leading to bacterial death. ⁴ Bacteriocins have been reported to inhibit important animal and plant pathogens, such as Shiga toxin‐producing E. coli (STEC), enterotoxigenic E. coli (ETEC), MRSA, VRE, Agrobacterium, and Brenneria spp. ⁷ Studies have found that 20 different E. coli strains could produce colicin with inhibitory activity against five different Shiga toxin‐producing E. coli strains (O26, O111, O128, O145, and O157: H7). In humans, this E. coli strain (STEC) could cause diarrhea and hemolytic uremic syndrome. E. coli strains, producing colicins E1, E4, E8‐J, K, and S4, were shown in a study to significantly inhibit the growth of STEC in a simulated cattle rumen environment (…). Cutler et al. ²³⁷ examined purified colicins E1 and N in vitro against enterotoxigenic E. coli F4 (K88) and E. coli F18, inducing post‐weaning diarrhea in piglets. In addition, purified colicin E1 protein was mixed into the diet of young pigs.

11.2.2. Colicin‐like bacteriocins

CLBs (colicin‐like bacteriocins) target strains closely related to the producer bacteria usually of the same species and have species‐specific names; colicins, klebicins, and pesticins are derived from E. coli, Klebsiella, and Yersinia pestis, respectively. S‐type pyocins (named after the second part of the name P. pyocyanea) are formed by more than 70% of Pseudomonas strains. CLBs are modular proteins that are protease‐resistant and contain domains involved in receptor binding, translocation, and cytotoxicity. ²³⁸

11.2.3. Tailocins

Tailocins, also known as high molecular mass bacteriocins, are similar to the tail structures of Myoviridae and Siphoviridae bacteriophages. Most Gram‐negative and Gram‐positive bacteria have tailocin gene clusters in their genomes. The contractile tail of P2‐like temperate enterophages is morphologically and genetically similar to R‐type pyocins. Tailocins, unlike CLBs, are not protease‐resistant and are not classified as immunity proteins. The mechanisms of resistance to tailocins are unknown; however, it is thought to be mediated by a change in the cell surface receptors recognized by tailocins. ²³⁸

11.2.4. Microcin

In addition to colicins, E. coli strains could produce microcins, which are smaller than colicins and have more properties in common with bacteriocins produced by Gram‐positive bacteria, such as thermostability, protease resistance, relative hydrophobicity, and resistance to extreme pH. ²³⁹ So far, 14 microcins have been discovered, but only seven have been isolated and thoroughly characterized. Microcins are low molecular weight (10 kDa), ribosomally synthesized, hydrophobic, antimicrobial peptides that differ from high molecular weight colicin proteins (25–80 kDa). Microcins are made up of N‐terminal leader and core peptides and are formed as precursor peptides. Microcins are primarily produced by Enterobacteriaceae, which are highly resistant to heat, pH, and protease. Microcins have a variety of bactericidal mechanisms, including pore formation, nuclease functions such as DNase and RNase, and inhibition of protein synthesis or DNA replication. No microcin gene cluster has a corresponding lysis gene; microcins are secreted outside the bacteria through the Type I ABC (ATP‐binding cassette) transporter secretion system, which is made up of a variety of proteins. ²⁴⁰ According to their molecular masses, disulfide bonds in their structure, and post‐translational modifications, microcins are divided into two classes. Class I microcins, such as microcins B17, C7‐C51, D93, and J25, are post‐translationally modified peptides with a low molecular weight (less than 5 kDa). Class II microcins have a higher molecular weight (5–10 kDa) than Class I microcins. Class II microcins are further classified into two subclasses: Class IIa and Class IIb. To synthesize and assemble functional peptides, Class IIa microcins, such as microcins L, V, and N, require three separate genes. Microcins in class IIb, such as microcins E492, M, and H47, are linear peptides with/without C‐terminal post‐translational modifications. ²⁴¹ Cursino et al. (2006) examined simultaneous administration of probiont and enteric pathogen S. flexneri to germ‐free mice, which resulted in a strong inhibition of the pathogen. The synthesis of microcin C7 as well as colicins E1 and Ib was responsible for the observed inhibition. Inhibition of S. flexneri was mediated by microcin C7 production, while colicins E1 and Ib acted as a stabilization mechanism. ²⁴²

11.3. New bacteriocin

Bacteriocins are ribosomally synthesized peptides produced by lactic acid bacteria (LAB), which have the potential to be used as food preservatives as well as antibiotics against multidrug‐resistant pathogens. ⁶⁰ The discovery of new bacteriocins with different properties indicates that there is still a lot of information to be understood about these peptide antibiotics. In this review, articles entitled with new bacteriocins from 2014 to 2020 were investigated (Table 9). Newly identified bacteriocins may differ in many respects, including the type of classes and subgroups to which they belong, biosynthetic mechanisms, structural characteristics, modes of antimicrobial action, and sources of isolation. Ahmad et al. ²⁴³ investigated a new bacteriocin produced by Lysinibacillus with the potential to prevent the growth of foodborne bacterial and fungal pathogens, especially B. pumilus producing pumilacidins toxin. Given that 14 novel species of Lysinibacillus have been identified so far, none of which have been able to act against B. pumilus. It would be beneficial to look for new bacteriocin‐producing LAB in the gastrointestinal tracts of different marine animals because they have already been adapted to a seafood environment. ²⁴⁴ Zhang et al. ⁴⁹ discovered PE‐ZYB1 as a new bacteriocin generated by P. pentosaceus zy‐B, isolated from Mimachlamys nobilis, with antimicrobial activity against L. monocytogenes. This bacteriocin could be used in the seafood industry as an important weapon against marine animal‐associated bacteria. ²⁴⁵ Some bacteriocins have a high specific activity, making them a good candidate for use in clinical cases against multidrug‐resistant species because they could function at low concentrations with high specificity. ²⁴⁶ They offer a possible solution to combat against MDR pathogens. Advances in science and technology to identify and purify bacteriocins make it possible to discover new bacteriocins that could control undesirable microorganisms (causing spoilage and pathogenesis).

TABLE 9.

Characteristics of new bacteriocins

Bacteriocin	Species and strain	Source	Mol. wt. (kDa)	Heat stability range	pH Stability range	Stability	Sensitivity	Production phase	Inhibitory activity spectrum	Reference
PE‐ZYB1	Pediococcus pentosaceus zy‐B	Intestine of Mimachlamys nobilis	2.02 (LC‐MS/MS)	At 121°C for 20 min	2.0–7.0	Papain Pepsase	Trypsin	MRS (48 h)	L. monocytogenes, S. hemolyticus S. aureus V. parahemolyticus, E. coli, E. aerogenes, P. aeruginosa B. subtilis B. cereus	49
Bacteriocin SLG10	Lactobacillus plantarum SLG10	Kombucha	1.4 (MALDI‐TOF‐MS)	(−)	2.0–7.0	Trypsin Pepsin	Proteinase K Chymotrypsin Pepsin	MRS (30 h)	B. subtilis B. cereus B. megaterium M. luteus B. thermosphacta C. butyricum S. aureus L.innocua L. monocytogenes E. coli	247
Bacteriocin SF1	S. flexneri serotype 2a	Dysenteric diarrhea	66 (glycine SDS‐PAGE)	At 76–80°C for 30 min	2 to 7	Trypsin α‐chymotrypsin Pepsin proteinase K papain	Proteinase K Papain	BHI (24 h)	E. coli B. fragilis	248
Un name	Lysinibacillus JX402121	Spoiled fruits and vegetable waste	51 (SDS‐PAGE)	up to 80°C temperature	4 to 9	Metal ion Amylase Lipase Surfactants Solvents	Proteinase K Pepsin Trypsin	MRS (48 h) aerobically	B. pumilus B. pumilus B. subtilis S. epidermidis S. aureus L. monocytogenes M. luteus B. cereus P. aeruginosa A. niger A. fumigatus F.oxysporium A. flavus T. viridae	243
BacBS2	Bacillus velezensis BS2	Meongge Jeotgal	6.5 (Tricine‐SDS PAGE)	At 80°C for 15 min	4–9	Pepsin Trypsin	Protease Proteinase K	LB	L. monocytogenes B. cereus	249
Subtilin L‐Q11	Bacillus subtilis L‐Q11	Orchard Soil	3.6 (MALDI‐TOF‐MS)	At 60°C for 15 min or 80°C for 30 min	2 to 7	Detergents	Trypsin Chymotrypsin Proteinase K Pepsin	LB	B.amyloliquefaciens L. lactis L. plantarum S. aureus E. faecalis S. aureus ATCC 29213 Bacillus spp	250
Bacteriocin CAMT2	Bacillus amyloliquefaciens ZJHD3‐06	Epinephelus areolatus	(−)	(−)	(−)	(−)	(−)	Modified tryptone glucose extract	L. monocytogenes ATCC 19111	251
Virgicin	Virgibacillus sp. strain AK90	Saltpan	2.4 (MALDI analysis)	At 100°C for 15 min	4 to 8	(−)	Trypsin Proteinase K	NB (24 h) Logarithmic phase	M. luteus MTCC 106 S. aureusMTCC 1430 S. aureus MTCC 96 B. subtilis MTCC 121 biofilm formation of Enterococcus faecalis	252
Gassericin S	L. gasseri LA327	Large intestine tissue in humans	5.4	At 121°C for 15 min	2–10	(−)	Proteinase K Trypsin a‐chymotrypsin	MRS	(−)	253
Plantaricin LPL−1	Lactobacillus plantarum LPL−1	Fermented fish	4.4 (MALDI‐TOF‐MS)	At 121∘C for 20 min	2–10	EDTA Tween 20 Tween 80 Urea	Pepsin Papain Proteinase K trypsin Chymotrypsin	MRS broth for 32 h at 37°C (exponential growth phase at 4 h)	S. aureus L. monocytogenes B. pumilus B. amyloliquefaciens E. faecalis L. plantarum L. delbrueckii, Lb. bulgaricus L. Salivarius, L. lactis	48
Bacteriocin DY4‐2	L. plantarum	Cutlass fish	1.5 (MALDI‐TOF‐MS)	At 121 °C for 30 min	2.5–5.5	(−)	Pepsin Trypsin Papain	MRS broth at stationary phase after 24 h incubation	Gram‐negative bacteria: P. fluorescens P001 P. fluorescens PF−04 L. monocytogenes19115 P. aeruginosa 9027 Shewanella putrefaciens 8071 V. harveyi BB107 Psychrobacter sp. 00052 Gram‐positive bacteria: Bacillus cereus 63301 B.licheniformis 11091	254
Plantaricin JY22	L.plantarum JY22	Golden carp intestine	4.1	At 121 °C for 20 min	2.5 to 5.5	Amylase	Nutrase Papain Pepsin	MRS (24 h)	Bacillus cereus	255
Plantaricin ZJ316	L.plantarum ZJ316		2.3	At 121 °C for 30 min	2.0 to 10.0		α‐chymotrypsin Trypsin Proteinase K	MRS	S.aureus E. faecalis M.luteus B. subtilis P. aeruginosa P. putida E. coli Acetobacter aceti, Salmonella enterica Vibrio parahaemolyticus L. monocytogenest Listeria welshimeri	256
Plantaricin GZ1‐27	L. plantarum WCFS1	Kipper of Dong	0.97 (MALDI‐TOF/MS)	At 80°C for 30 min	2.0–6.0	(−)	Proteinase K Papain Trypsin Pepsin	MRS (36 h)	Spoilage bacteria: B. thermosphacta P. fluorescens A. baumannii Pathogenic bacteria: B. cereus S. aureus S. typhimurium L. monocytogenes E. coli	257
Bifidoadocin	B. adolescentis	(−)	14.6	At 90 °C for 15 min	3–8	(−)	Chymotrypsin Pepsin Papain	(−)	K.pneumoniae A. baumanii Staphylococcus spp. Salmonella spp. P. aeruginosa A.hydrophila	210
Fermencin SA715	Lactobacillus fermentum GA715	Goat milk origin	1.8 (MALDI‐TOF)	At 40–90°C for 30 min	2–7	Lysozyme Lyticase Catalase	Proteinase K Peptidase Trypsin α‐chymotrypsin Protease	MRS (18 h)	M.s luteus ATCC 10240 Corynebacterium spp. GH17 P.aeruginosa PA7 S. aureus RF122 L. monocytogenes NCTC10890 S. mutans GEJ11 S. equisimilis ATCC 12388, S. sanguinis ATCC 10556 B.cereus ATCC 14579 E.coli UT181	258
Salivaricin mmaye1	Lactobacillus salivarius SPW1	Human feces	1.2 (MALDI‐TOF)	At 121°C for 15 min	2–10	Detergents Protease	Pepsin Trypsin α‐chymotrypsin Protease Proteinase	MRS (18 h)	Streptococcus Lactococcus Listeria Staphylococcus Corynebacterium Pseudomonas Escherichia Micrococci Lactobacillus Enterococci	259
Pentocin MQ1	Lactobacillus pentosus CS2	Coconut	2.1 (MALDI‐TOF)	At 121°C for 15 min	2–5	Detergents Protease	Proteinase K Pepsin Proteinase Trypsin α‐chymotrypsin Protease	MRS broth at 37°C for 20 h	L. monocytogenes NCTC 10890 M. luteus ATCC 10240 B. cereus ATCC 14579 S. pyogenes ATCC 12344 S. aureus RF122 P. aeruginosa PA7 E. faecium ATCC 19434 E. faecium ATCC 27270 E. faecium ATCC 27273 E. faecium ATCC BAA‐2318 E. faecium ATCC BAA‐2127 E. faecium ATCC 6569 E. faecium ATCC 25307 E. faecium ATCC 349	260
Plantaricyclin A (PlcA)	Lactobacillus plantarum NI326	Olives	5.5 (MALDI‐TOF)	At 100°C for 10 min	2–10	Proteases	Proteinase K Pronase	MRS broth supplemented with 0.8% bacteriological agar	A. acidoterrestris sp1 Lb. bulgaricus UCC Pediococcus inopinatus 1011 Lactococcus lactis HP UCC L. lactis KH UCC L. lactis MG1363 UCC L. lactis RT28 UCC L. lactis NZ9000	261
Bacteriocin SKI19	Lactobacillus plantarum subsp. plantarum SKI19	Sai krok e‐san mu”	2.5	At 121°C for 15 min	2–10	(−)	α‐chymotrypsin Trypsin Proteinase K Pronase E	MRS (24 h) early stationary phase	L. monocytogenes DMST 17303 E.coli DMST 4212 S. aureus DMST 8840	262
Leucocin C−607, 607A	Leuconostoc pseudomesenteroides 607	Persimmon fruit	C−607 (4.6) 607A (3 and 3.1)	At 121°C for 15 min (C−607) At 80/90°C for 30 min (607A)	(−)	(−)	Proteinase K Trypsin	MRS (72 h)	Multidrug‐resistant S. aureus L. casei ATCC 393 MRSA GIM 1.771 S. dysenteriae CGMCC 1.1869 E. coli O157:H7 GIM 1.707 B. subtilis CGMCC 1.1627 E. faecalis ATCC 51575, L.monocytogenes ATCC 19112 M. luteus CGMCC 1.2299 P. aeruginosa CGMCC 1.1785	263
Plantaricin DL3	Lactobacillus plantarum DL3	Chinese Suan‐Tsai	4.1	At 121°C for 15 min	2.5–5.5	α‐‐amylase	Pepsin Trypsin Papain	MRS (24 h)	P. aeruginosa. L. monocytogenes P. aeruginosa S. putrefaciens Psychrobacter sp. Gram‐positive S. aureus B. cereus B.licheniformis P. fluorescens, S. putrefaciens	264
Mejucin	Bacillus subtilis SN7	Meju	(−)	(−)	(−)	Enzymes (α‐amylase or lipase) solvent (Ethanol Acetonitrile, Acetone, Methanol)	Proteinase K Protease α‐Chymotrypsin Pepsin Aminopeptidase I Carboxypeptidase Mercaptoethanol	TSB at 37 C for 24 h	B. cereus strains L.monocytogenes S. aureus ATCC 29213 M. luteus ATCC 15307	265

12. THE PROBIOTIC APPLICATION OF BACTERIOCINS

12.1. The GI tract

The human gastrointestinal tract is a complex environment in which the intestinal microflora and the host maintain a delicate balance. The microflora acts as a primary stimulus for the development of the mucosal immune system. The two main genera of lactic acid bacteria, including Lactobacillus and Bifidobacterium, dominate the intestinal flora with 56 Lactobacillus and various Bifidobacterium species. In in vitro, the majority of these organisms have been shown to produce bacteriocins. A compelling in vivo analysis demonstrated the activity of Ligilactobacillus salivarius strain UCC118 that produced a potent broad‐spectrum bacteriocin (Abp118) active against the foodborne pathogen L. monocytogenes. ²⁶⁶ In a study, an enterohemorrhagic strain of E. coli and a strain of L. monocytogenes were shown to significantly inhibit an enterohemorrhagic strain of E. coli and a strain of L. monocytogenes in mice, most likely due to bacteriocin activity. ²⁶⁷ The release of bacteriocins inhibiting H. pylori, as a human pathogen that causes severe gastroduodenal diseases, has been chiefly studied in lactobacilli strains. Anti‐H. pylori activity of probiotic strains L. johnsonii LA1 and L. acidophilus LB was identified by Gillor et al. (2008). According to the results, when H. pylori was attached to intestinal epithelial cells in both cases, inhibitory activity was retained. Also, oral administration of L. acidophilus LB in mice protected the animals from H. felis infection. This probiotic bacterium (LB) was also shown to inhibit gastric colonization and prevent gastric inflammation. Oral intake of live bacteria by H. pylori‐positive school children resulted in a significant decrease in urease production, while administration of L. johnsonii LA1 supernatant to adult patients colonized by H. pylori significantly decreased infection. ²⁶⁸

12.2. Treatment of pathogen‐associated diseases

Stern et al. (2006) purified Class II low molecule mass bacteriocin OR‐7 from L. salivarius strain NRRL B‐30514, which was potent in inhibiting C. jejuni causing human gastroenteritis. OR‐7 was resistant to lysozyme and lipase therapy, heat up to 90°C, and pH levels of 3.0 to 9.1. For chicken feed, purified OR‐7 was encapsulated in polyvinylpyrrolidone. In the cecal material of OR‐7‐treated chickens, the population of C. jejuni decreased by at least one million fold compared with chickens not given OR‐7 supplementation. These results suggest the high potential of nisin, OR‐7, and other bacteriocins for use as suitable alternatives to antibiotics in poultry and other animal feeds. ²⁶⁹ Only a few bacteriocins have been tested against C. difficile infection so far (CDI). The mode of delivery of bacteriocins to the colon must be carefully analyzed when using bacteriocins as an alternative/adjunctive therapeutic choice for CDI. Encapsulation of bacteriocins could be a way to avoid the protease effect.

12.2.1. Thuricin CD

Thuricin CD is a recently identified bacteriocin with effective narrow‐spectrum inhibitory activity against C. difficile. The primary advantage of thuricin CD is that its antimicrobial activity is mostly restricted to C. difficile and has little or no impact on other gut microorganisms. This was demonstrated in a study using a human distal colon model and a high‐throughput sequencing approach, which revealed that thuricin CD had minimal impact on the numbers of Firmicutes, Bacteroidetes, and Proteobacteria compared with vancomycin and metronidazole, eliciting a decrease in Firmicutes and Bacteroidetes numbers as well as an increase in Proteobacteria number. ²⁷⁰

12.2.2. Lacticin 3147

Lacticin 3147 is a 2‐peptide antibiotic produced by L. lactis DPC 3147. Lacticin 3147 was shown by Rea et al. (2007) to trigger fast lysis of log‐phase C. difficile cells, measured by quantifying the release of acetate kinase. The addition of lacticin 3147 at a high concentration of 6 mg/ml resulted in a decrease in C. difficile ATCC 43593 cell number from 106 cfu/ml to zero within 2 h. Subsequent studies displayed that the use of lacticin 3147 resulted in a decrease and increase in Firmicutes and Proteobacteria numbers, respectively. ²⁷¹ Actagardine A is a 19‐amino acid lantibiotic with powerful antimicrobial activity against Gram‐positive bacteria, including C. difficile. NVB302 is a semi‐synthetic Type B lantibiotic extracted from actagardine, which is effective against C. difficile and performs better than vancomycin. ⁵⁹

12.2.3. LFF571 (GE2270 derivative)

GE2270 is a thiopeptide bacteriocin that inhibits translation in bacteria. LFF571 is a semi‐synthetic derivative of thiopeptide GE2270, developed by Novartis Co., which displays antimicrobial activity against a range of Gram‐positive bacteria, including C. difficile. In vivo human activity of LFF571 against C. difficile was compared with vancomycin in a survey on gold Syrian hamster models. Only 2.2% of hamsters experienced recurrence in the case of treatment with 5 mg/kg of LFF571, whereas 37.8% of hamsters which survived at the termination of treatment with 20 mg/kg of vancomycin experienced recurrence. ²⁷² Durancin 61A as a glycosylated bacteriocin produced by E. durans 61A was investigated in a study by Hanchi et al. (2017) and shown to be active against clinical drug‐resistant C. difficile, E. faecium, VRE, and MRSA. In their study, durancin 61A exhibited bactericidal activity and acted on the bacterial membrane with a pore‐formation mechanism, including pore and vesicle formation, cell disruption, and loss of membrane integrity and cytoplasm content. The observed increase in durancin 61A MIC for nisin‐ and pediocin‐resistant variants could be probably due to their similar mode of action on bacterial membrane. The absence of cross‐resistance in durancin‐resistant variant of E. faecalis ATCC 27275 suggests a different site of action for this bacteriocin. The susceptibility of vancomycin‐resistant variants to durancin 61A could be due to the altered cell wall physiology and metabolism of vancomycin‐resistant variants. ²⁷³

12.2.4. Pediocin PA‐1

One of the main subclasses of bacteriocins is the pediocin family, a title derived from pediocin PA‐1 as the first and extensively studied member of this family. The pediocin family members are small, heat‐stable, membrane‐active peptides that contain no lanthionine and possess a YGNGVXC consensus motif. Members of this class have several features in common, considering a very strong antimicrobial activity against L. sakacin P and L. sakacin G. ²⁷⁴ It has been shown that L. curvatus FS 47 produces curvaticin FS47 active against L. monocytogenes. Besides the strain L. plantarum C11 as the first strain isolated from a plant source, four other strains of L. plantarum, including WCFS1, NC8, 51, and J23, have been found to harbor YGNGVQCilar bacteriocin locus in their genomes, peculiarly plantaricin A (PlnA) as a cationic peptide pheromone with membrane permeabilizing activity. ²⁷⁵ The 2‐element Class II bacteriocins derived from L. salivarius isolated from mammals have been characterized as follows: ABP‐118 (produced by human intestinal probiotic strain L. salivarius UCC118), L. salivaricin CRL 1328 (produced by L. salivarius CRL 1328 strain isolated from the healthy human vagina), and salivaricin P (produced by porcine intestinal probiotic strain L. salivarius DPC6005). ²⁷⁶ FK22, OR7, L‐1077, and SMXD51 bacteriocins derived from L. salivarius isolated from chicken intestines or intestinal contents (L. salivarius K7, L. salivarius NRRL B‐30514, L. salivarius 1077 NRRL B‐50053, and L. salivarius SMXD51) have been defined as one‐factor Class II bacteriocins. ²⁷⁷ ABP‐118 is an appealing broad‐spectrum antimicrobial substance since it could inhibit several foodborne and medically notable pathogens, such as Bacillus, Listeria, Enterococcus, and Staphylococcus genera, without a clear antagonistic activity toward related LAB. ABP‐118 is a Class IIb two‐peptide bacteriocin consisting of Abp118α and Abp118β. The Abp118α peptide possesses inhibitory activity when concentrated, and the presence of the Abp118β peptide enhances this activity; ABP‐118 does not have the related bacteriocin activity on itself. ²⁷⁸ LS1 is a human bacteriocin, produced by L. salivarius BGHO1 as a human oral isolate, with antagonistic activity against S. mutans, S. pneumoniae, S. aureus, E. faecalis, M. flavus, and S. enteritides. ²⁷⁶ Wu et al. ²⁵¹ conducted a study to investigate the mode of action of bacteriocin CAMT2, produced by B. amyloliquefaciens ZJHD3‐06, against highly pathogenic L. monocytogenes ATCC 19111; it exhibited inhibitory activity against important food spoilage and foodborne pathogens. As a member of acyldepsipeptide antibiotics, ADEP‐1 activity is through interrupting protein metabolism in the bacterial cell by eliciting over‐activation of intracellular caseinolytic ATP‐dependent proteases. Therefore, interruption of intracellular protein metabolism leads to cell division, differentiation, sporulation impairment, and finally bacterial cell death. Interestingly, it has been shown that CD proteases targeted by acyldepsipeptide antimicrobials are also related to the intracellular systems sigma factors σ (E) and MazEF, which play a key role in CD sporulation. Given the bactericidal activity of ADEP‐1 against Gram‐positive bacteria and caseinolytic proteases in CD, as the potential target of this compound, some authors have recently proposed the use of ADEP‐1 and other acyldepsipeptide antimicrobials to treat CDI, either alone or in combination with other antimicrobial classes. ²⁷⁹

13. FOOD TECHNOLOGY

In food technology, nisin as the first antibacterial peptide found in LAB is produced by L. lactis. It is also a commercial bacteriocin marketed as Nisaplin^®, which is used as a food preservative against contamination with microorganisms. It is the only bacteriocin approved by USFDA for use as a preservative in many food products and licensed as a food additive in over 45 countries. Another commercially available bacteriocin is pediocin PA‐1 marketed as Alta^® 2341, which inhibits the growth of L. monocytogenes in meat products. Enterocin AS‐48 is used in cider, fruit and vegetable juices, and canned vegetables for contamination inhibition. Enterocins CCM4231 and EJ97 are used in soy milk and zucchini purée to suppress contamination, respectively. ²⁸⁰ The use of bacteriocins as food preservatives may be beneficial in several aspects: (i) to decrease the risk of food poisoning, (ii) to decrease cross‐contamination in the food chain, (iii) to improve the shelf life of food products, (iv) to protect food during temperature‐abuse episodes, (v) to decrease economic losses due to food spoilage, (vi) to reduce the level of chemical preservatives added, (vii) to reduce the intensity of physical treatments in order to better preserve food nutritional value and decrease processing costs, and (viii) to provide alternative preservation methods for "novel food" in order to meet the demands of consumers for fresh‐tasting, lightly preserved, ready‐to‐eat food products. ²⁸¹

14. CONCLUSION

Given their broad‐spectrum and potent inhibitory activity, this study results indicated that lactic acid bacteria are able to exert antagonistic activity against pathogenic bacteria in vitro and in vivo. This study provides a comprehensive overview of what is known about LAB bacteriocins, especially their properties, classification, biology, sources, biosynthesis, potential applications, activity against foodborne pathogens, impact on antibiotic‐resistant bacteria, mode of action, genetic determinants, range of activity, and factors affecting their production. Many strains of lactic acid bacteria related to food groups could produce bacteriocins or antibacterial proteins that are highly effective against foodborne pathogens, such as S. aureus, P. fluorescens, P. aeruginosa, S. typhi, S. flexneri, L. monocytogenes, E. coli O157:H7, K. pneumoniae, and C. botulinum. A wide range of bacteria belonging primarily to the genera Bifidobacterium and Lactobacillus, even some gram‐negative bacteria like E. coli, have been characterized with different health‐promoting attributes. The frequency and variety of bacteriocin production vary greatly between populations of gram‐positive and gram‐negative bacteria. Extensive and in‐depth studies have been performed on gram‐positive bacteria and also relatively few on gram‐negative bacteria. Production of two or more bacteriocins by one cell in gram‐negative bacteria is a common phenomenon, at least in E. coli. More research is needed to understand the nature of the fitness benefits of producing multiple bacteriocins and how to optimally use bacteriocins in gram‐negative bacteria as alternatives to traditional antibiotics and to create and select bacterial strains for use as probiotics.

Studies results describe bacteriocins as supplements for antibiotics due to their high stability, no side effects, and potential to induce a synergistic effect. In combination with antibiotics, bacteriocins act synergistically; they not only increase the efficiency of antibiotics and prevent the emergence of antibiotic‐resistant species but also reduce the side effects of antibiotics by lowering the concentration of antibiotics needed to eliminate bacteria. The results of recent studies on this topic show that bacteriocin as being a versatile antimicrobial with appreciable potency for utilization as biopreservatives, antibiotic alternatives, health‐promoting gut modulators, and animal growth promoters. One of the reasons for the positive trend toward bacteriocins is the overuse of antibiotics, especially broad‐spectrum antibiotics in medicine and food production, which is known as a microbiome disorder and for the accumulation and transfer of resistance genes in the intestinal microbial population. Man has been chosen.

According to the present study results, the correct selection of bacteriocin‐producing strains suitable for use in the food industry is very important. Thus, this emphasizes the necessity of investigating LAB bacteriocins to prove their beneficial and nutritional properties as well as inhibitory activity against the growth of functional pathogens, as they are potentially crucial for the final preservation of functional foods and for medicinal applications.

According to the present study results, the correct selection of bacteriocin‐producing strains suitable for use in the food industry is very important. Thus, this emphasizes the necessity of investigating LAB bacteriocins to prove their beneficial and nutritional properties as well as inhibitory activity against the growth of functional pathogens, as they are potentially crucial for the final preservation of functional foods and for medicinal applications.

CONFLICT OF INTEREST

The authors declare that there is no conflict of interest.

AUTHOR CONTRIBUTIONS

RG and MK conceived, designed, and supervised the study. AD and AA contributed to data collection, interpretation, and final approval of data for the work. AD and MM developed the first and final draft of the manuscript. EO and MT developed the second draft of the manuscript. ADE and MH designed and checked all figures and tables. All authors reviewed, contributed to the revisions, and finalized the drafts.

Darbandi A, Asadi A, Mahdizade Ari M, et al. Bacteriocins: Properties and potential use as antimicrobials. J Clin Lab Anal.2022;36:e24093. doi: 10.1002/jcla.24093

DATA AVAILABILITY STATEMENT

All relevant data are included in the manuscript.