Bacteriophages Against Bacterial Infections in Poultry Systems: A Scientometric Review

Abstract

Poultry production faces challenges from bacterial infections, aggravated by antibiotic resistance, affecting bird welfare and the industry’s economy. Bacteriophages show promise as a solution, but their use in poultry systems is still limited. This study uses scientometric analysis to investigate the incidence of bacterial infections in poultry systems and bacteriophage application trends. The Web of Science database was used, and the articles were refined by searching for keywords that included the most rep orted bacteria in the different phases of poultry farming and the application of phages. The articles were analyzed using the CiteSpace and Excel software, allowing the evaluation of publication trends, influential countries, and correlations with antimicrobial resistance and the use of bacteriophages. Results highlight Escherichia coli prevalence in poultry systems and reveal a correlation between the number of publications and poultry productivity, with the United States and China leading both aspects. Findings offer insights into bacterial control gaps in poultry systems, underscoring the need for further research and practical strategies.

Graphical Abstract

Introduction

The poultry sector has great socioeconomic importance and is responsible for providing food and jobs for millions worldwide. According to estimates from the Food and Agriculture Organization (FAO) of the United Nations,¹ chicken meat is the leader in the world meat trade. It is further estimated that poultry production will account for over 55% of meat production growth by 2031, with poultry meat projected to constitute 47% of the protein consumed from meat sources (FAO¹). The short production cycle, low costs associated with handling, and nutritional characteristics turn chicken meat into one of the world’s most consumed.^2,3

The poultry industry uses intensive rearing systems to obtain substantial amounts and high stocking densities to meet the increasing demand. However, the barns overcrowding provides an environment conducive to emerging infections that inevitably affect productivity.⁴ Infectious diseases result from a nonfriendly host–parasite relationship in a microscopic environment. In poultry habitats, these infections are mainly due to pathogens, stress, injuries, and deficiency of vital nutrients, leading to the bird’s death.⁵ Among these infections, bacterial diseases are responsible for many fatalities in poultry farming systems, representing approximately half of the no-outbreak mortality, reducing poultry productivity, affecting the quality of meat and eggs, and consequently causing economic losses.^6,7 Niemi⁸ reported that salpingo peritonitis, a disease primarily caused by Escherichia coli, can lead to a loss of approximately US$0.58 per bird. In addition to the economic impact, the search to improve poultry health and welfare underscores the need to understand how bacterial infections occur and disseminate in poultry farming systems, which species are the most common, and how these infections can be treated or prevented.

Recently, bacteriophages, viruses that infect bacteria exclusively, have drawn attention as an innovative alternative to complement the disinfection approaches in poultry farming systems.⁴ Wong et al.⁹ reported a reduction in bacteria concentration after artificially inoculating 6-day-old bacteria-free chicks with Salmonella typhimurium and bacteriophages. The decline of other Salmonella strains is also shown by Ge et al.,¹⁰ who observed a reduction of S. enteritidis and S. pullorum in chicken skin using the S55 phage. Furthermore, the in vitro use of bacteriophages to reduce E. coli biofilm and to combat the incidence of avian pathogenic E. coli (APEC) has already been reported.^11,12

Nevertheless, the study of these viruses in live animals is still embryonic, and it is necessary to understand the strengths and gaps better so that technological application is possible. A way of studying current trends in a scientific field is through scientometric approaches. This method allows the identification of the main theories and research related to a search area.¹³ Considering that there are no systematic reviews on this specific subject, this work aimed to carry out a scientometric analysis using CiteSpace and Excel to assess the incidence of bacterial infections in poultry systems. The research also allowed us to verify the trends and relevance of bacteriophages as an alternative treatment in poultry chains, aiming to answer the following questions:

Q1.

What is the chronological growth of published articles on bacterial infections and bacteriophage application?

Q2.

What are the most influential countries on this topic? To what can this relevance be attributed?

Q3.

Based on the keywords co-occurrence network, what is the knowledge structure of bacterial infections and bacteriophages in poultry systems?

Q4.

How can the incidence of antimicrobial resistance and the use of bacteriophages be correlated?

Q5.

What are the main trends and gaps in research on bacteriophages in poultry systems?

Methods

Literature search

The data were obtained from the Web of Science (WoS) core collection and organized into two lists. The mentioned platform has a vast database of scientific publications and is a valuable data source for scientometric analysis.^14,15 The first list (i) looks for the incidence of bacterial infections in poultry systems, considering the most reported bacteria in different stages of poultry breeding. This list is identified as “bacterial outbreaks” (BAC). The second list (ii), named bacteriophages or phages (PHA), was created using the same keywords of BAC but adding the term “phages” to unfold the trends and relevance of using bacteriophages.

The literature search used the topic search (TS) strategy, including article titles, abstracts, author keywords, and keywords plus. The Boolean operator was used to combine search terms as follows:

• i)BACTS=((“poultry” OR “Broiler” OR “Laying hen” OR “Broiler litter” OR “Chicken” OR “Chicks” OR “Fowl” OR “Hen” OR “poultry bed” OR “poultry litter”) AND (“enterobacteria” OR “Escherichia coli” OR “E. coli” OR “Campylobacter spp.” OR “Salmonella spp.” OR “Yersinia enterocolitica” OR “Y. enterocolitica” OR “Serratia marcescens” OR “S. marcescens” OR “listeria monocytogenes” OR “L. monocytogenes” OR “Streptococcus aureus” OR “S. aureus” OR “Shigella boydii” OR “S. boydii” OR “Shigella flexneri” OR “S. flexneri” OR “Shigella dysenteriae” OR “S. dysenteriae” OR “Staphylococcus aureus” OR “MRSA” OR “Pseudomonas aeruginosa” OR “P. aeruginosa”))
• ii)PHATS=((“poultry” OR “Broiler” OR “Laying hen” OR “Broiler litter” OR “Chicken” OR “Chicks” OR “Fowl” OR “Hen” OR “poultry bed” OR “poultry litter”) AND *phage* AND (“enterobacteria” OR “Escherichia coli” OR “E. coli” OR “Campylobacter spp.” OR “Salmonella spp.” OR “Yersinia enterocolitica” OR “Y. enterocolitica” OR “Serratia marcescens” OR “S. marcescens” OR “listeria monocytogenes” OR “L. monocytogenes” OR “Streptococcus aureus” OR “S. aureus” OR “Shigella boydii” OR “S. boydii” OR “Shigella flexneri” OR “S. flexneri” OR “Shigella dysenteriae” OR “S. dysenteriae” OR “Staphylococcus aureus” OR “MRSA” OR “Pseudomonas aeruginosa” OR “P. aeruginosa”))

Scientometric analysis

CiteSpace (5.8.R3), an open-access software based on Java, was used to visualize and map keyword co-occurrence networks, countries, and research areas, besides interpreting the scientific arena’s trends and relevance. The infographics generated by the software have a node representing an item (country, keyword, or other) and links connecting one node to another, representing their co-occurrence or co-citation. The chronological order of co-occurrence links can be observed from a spectrum of colors, with blues being the oldest and oranges the newest. In addition, purple circles refer to good centrality and red circles represent a citation burst and a sudden increase in the frequency of a specific type of event in a period.¹⁶

Quantitative projection of publications for the list (PHA)

To quantitatively analyze the development of future publications from the list PHA, the logistic model expressed in Equation (1) was used and solved numerically with the help of the software Statistica (StatSoft V.12.5 Trial). To find the curve’s inflection point, which marks the change from the growth phase to maturity 0−, we did the first derivative of Equation (1). The annual change criterion of less than 1% of the cumulative was used to establish the beginning of the decline phase:

$${NA}_{(t)}=\frac{{NA}_{\max }}{1+e^{-\alpha (t-\beta )}}$$ (1)

NA_(t) represents the number of articles published cumulatively over the years, t represents the time variable, and t₌₁ is the year 1979. The year 1979 was used, considering that publications related to the PHA list began that year. Time should be entered into the Equation sequentially, not the year of publications, “α” and “β” are dimensionless parameters of the model, and AN_(max) is the maximum value of publications predicted in this study.¹⁷

Results and Discussion

We found 8,165 documents to list BAC from 1958 to 2022, whereas 436 results were obtained between 1979 and 2022 for the PHA list. The searches covered articles, review articles, abstracts, and books and were manually refined by reading the title and abstract, excluding documents unrelated to the topic of interest. After refinement, 2,175 documents were used for the scientometric analysis for the list BAC and 97 for the list PHA, as shown in Figure 1. These results were analyzed separately and compared to visualize and understand the trends of each line of research and the commonalities between them.

FIG. 1.

Search flow for the lists BAC and PHA. *Some articles do not have all the necessary data to be processed in the software and some can be duplicated articles. BACTS = ((“poultry” OR “Broiler” OR “Laying hen” OR “Broiler litter” OR “Chicken” OR “Chicks” OR “Fowl” OR “Hen” OR “poultry bed” OR “poultry litter”) AND (“enterobacteria” OR “Escherichia coli” OR “E. coli” OR “Campylobacter spp.” OR “Salmonella spp.” OR “Yersinia enterocolitica” OR “Y. enterocolitica” OR “Serratia marcescens” OR “S. marcescens” OR “listeria monocytogenes” OR “L. monocytogenes” OR “Streptococcus aureus” OR “S. aureus” OR “Shigella boydii” OR “S. boydii” OR “Shigella flexneri” OR “S. flexneri” OR “Shigella dysenteriae” OR “S. dysenteriae” OR “Staphylococcus aureus” OR “MRSA” OR “Pseudomonas aeruginosa” OR “P. aeruginosa”)). PHATS = ((“poultry” OR “Broiler” OR “Laying hen” OR “Broiler litter” OR “Chicken” OR “Chicks” OR “Fowl” OR “Hen” OR “poultry bed” OR “poultry litter”) AND *phage* AND (“enterobacteria” OR “Escherichia coli” OR “E. coli” OR “Campylobacter spp.” OR “Salmonella spp.” OR “Yersinia enterocolitica” OR “Y. enterocolitica” OR “Serratia marcescens” OR “S. marcescens” OR “listeria monocytogenes” OR “L. monocytogenes” OR “Streptococcus aureus” OR “S. aureus” OR “Shigella boydii” OR “S. boydii” OR “Shigella flexneri” OR “S. flexneri” OR “Shigella dysenteriae” OR “S. dysenteriae” OR “Staphylococcus aureus” OR “MRSA” OR “Pseudomonas aeruginosa” OR “P. aeruginosa”)). BAC, bacterial outbreaks; TS, topic search.

Research relating bacteriophages to battle bacterial infections in poultry production has gained more attention recently, as shown in Figure 2. Publications from the past 5 years represent more than 40% of the total for both searches. This increase is probably related to the rise in poultry production in recent years. Intensive breeding systems meet the demand, increasing the incidence of bacterial infections and resistant bacteria and making treatment with less effective antibiotics.¹⁸

FIG. 2.

Number of publications in the BAC and PHA lists from 1958 to 2023.

In 2015, member countries of the World Health Organization adopted the Global Plan of Action on Antimicrobial Resistance to mobilize governments to fight against resistant bacteria. The plan is based on the concept of One Health, considering the relationship between animal, human, and environmental health as inseparable. The increase in research on bacterial infections in poultry farming systems could be related to efforts to adapt to the plan, as it is necessary to understand the pattern of these infections and the microorganisms involved.

The poultry sector stands out in relation to the use of antibiotics with a demand of approximately 148 mg/unit of population correction.¹⁹ Although antibiotics are an important tool to increase animal production and meet demand for food, the constant use of antimicrobials has raised concerns about the emergence of super resistant strains. In 2019, the World Health Assembly addressed the rational use of antibiotics in animals and the transfer of technology to prevent and control antimicrobial resistance.^20–22 This concern justifies the growing research on applying bacteriophages in animal husbandry systems as an alternative to reduce the use of antibiotics and combat antibacterial resistance.^23,24

The analysis of the keywords used by the authors to describe their research concept also shows the concern related to the incidence of resistant microorganisms. The expressions “antimicrobial resistance,” “antibiotic resistance,” and “resistance” appear 999 times among the publications of the BAC list. Figure 3A allows the visualization of the co-occurrence network of the 10 main keywords in the list BAC, where the nodes represent a keyword, and the lines that connect two nodes demonstrate the co-occurrence of two keywords. According to frequency, the main keywords are Escherichia coli (655), antimicrobial resistance (508), prevalence (426), poultry (384), strain (299), and gene (264). A thick red circle around “antibiotic resistance” can be observed, indicating an explosion of publications related to the topic in recent years.

FIG. 3.

Top 10 keywords (A) without phages (BAC) and (B) with phages (PHA).

Figure 3B shows the occurrence of keywords found for the list PHA, with the words Escherichia coli (24), poultry (21), infection (18), broiler chicken (18), and bacteriophage (18) being the most frequent. This indicates that the antibiotic growth promoters used in the agricultural sector are increasing the population of antibiotic-resistant bacteria.²⁵ As a result, there is growing interest in developing alternatives to maintain or improve the growth performance of farm animals.²⁶

E. coli, the most cited bacterium in the two analyzed lists, appears in Figure 3A with a purple halo indicating its centrality and influence when it comes to infections in poultry systems linked to words such as “antimicrobial resistance,” “infection,” and “antibiotic resistance.” This organism is the most common pathogen in the poultry environment, and virulent E.coli strains, such as APEC, are commonly found infecting the intestines of birds.²³ APEC can cause avian colibacillosis, one of the primary sources of mortality and morbidity associated with economic losses in the poultry industry worldwide.²⁷ Furthermore, E. coli is more susceptible to resistance than other bacteria and is a model for studying antimicrobial resistance worldwide.^28,29 This issue makes it more prevalent when dealing with infections in poultry farming systems, resulting in more studies that seek to understand these infections and find alternative ways, such as using bacteriophages to fight them.

The need to maintain productivity and avoid economic losses related to the increase of these bacterial infections also contributes to the rise in publications in recent years. Countries with the highest number of publications are also the largest poultry producers, as shown in Figure 4A and B. The United States, with 327 publications, is the world’s largest producer of poultry, followed by China (209) and Brazil (136), according to Brazilian Animal Protein Association.³⁰ This highlights that scientific research often goes hand in hand with economic interests.

FIG. 4.

(A) Geolocation of scientific publications without phages (BAC). (B) Top 10 countries and frequency of publications (BAC). (C) Network of collaborating countries (BAC). (D) Countries with the most powerful citation bursts (BAC).

Figure 4C reveals the collaboration network between the countries, with the more vital lines connecting the nations, meaning a greater coparticipation of publications. It is possible to observe a strong collaboration between the Netherlands, England, and the United States. The red circles in Figure 4C show the burst of citations, which indicate the countries with a sudden increase in the number of publications in recent years, as is the case of Egypt and Bangladesh, which show the most recent bursts as shown in Figure 4D. Other countries such as Pakistan and Bangladesh have also seen an increase in publications in recent years, however the number of publications is insignificant. In addition to frequency, co-occurrence, and burst, CiteSpace also allows observing centrality related to the influence of citations. However, the two generated lists did not present centrality, indicating that the publications have the same impact regardless of the country.

In the PHA list, the countries that published the most were the United States (22), China (13), Poland (9), South Korea (8), and Canada (6), as shown in Figure 5. The top 10 countries are related to the largest poultry producers and countries with higher technology and research investments regarding the bacteriophage’s application. Figure 5C shows a strong collaboration between countries and the burst of citations. The United States has had the most significant burst, with the explosion of publications occurring between 2001 and 2015, indicating that this subject was extensively researched and studied in the country for many years.

FIG. 5.

(A) Geolocation of scientific publications without phages (PHA). (B) Top 10 countries and frequency of publications (PHA). (C) Network of collaborating countries (PHA).

The scientometric analysis also allowed the ranking of the main subject categories related to bacterial infections in poultry systems and the use of phage to combat them, showing the research areas with the most significant scientific influence (Fig. 6). Observing Figure 6A related to the BAC list, it becomes evident that “Veterinary Sciences” is emphasized with a high frequency (731). Two other categories presented a relevant number of publications, “Microbiology” and “Agriculture, Dairy & Animal Science,” with a frequency of 618 and 377, respectively.

FIG. 6.

(A) Top 10 research areas in BAC list and (B) Categories with strong citation burst. (C) Top 10 research areas in PHA list.

However, the subjects with the highest frequency do not represent the most significant influence. The areas with the highest centrality, symbolized by the purple halo, were “Environmental Sciences” (0.35) and “Microbiology” (0.34), indicating that many of the publication’s areas are influenced by an environmental concern bias. Moreover, an insightful observation from burst citation analysis underscores changing trends in these subject areas over the years (Fig. 6B), revealing a discernible shift toward more applied research fields.

Figure 6C, which represents the PHA list, shows a change in the order of priority of the subject categories. The areas with major frequency were “Microbiology” (29) and “Agriculture, Dairy & Animal Science” (24). As in the BAC list, “Agriculture, Dairy & Animal Science” despite having many publications, does not have centrality, indicating its low influence in the field. On the contrary, “Biotechnology & Applied Microbiology,” which did not stand out in frequency (13), has the largest centrality (0.53). In other words, despite the low visibility of this area, there is a significant influence, which reflects the importance given to studies that address biotechnological applications of phages to combat bacterial infections in poultry systems. Another critical point to be highlighted is the frequency (19) and centrality (0.23) of “Veterinary Sciences” which indicate a trend in publications focused on in vivo applications as satisfactory phage efficiency in vitro does not guarantee therapeutic success in vivo.¹²

Although their first description dates back to the beginning of the last century, it was not until the 1980s that the use of bacteriophages in controlled studies with animals began to be published in the scientific literature.³¹ According to the S-curve shown in Figure 7, the 1980s also represent the emerging period of publications, lasting until approximately 2002, with 14 publications accumulated. Many simulation methods have been developed to predict the future of technologies. A product or technology usually goes through four stages: emergence, growth, maturity, and decay (saturation), which can be obtained by simulating S-curves.³² The S-curve is used to simulate a given technology’s development and evaluate its degree of maturity; it is not different from the number of publications on a given subject.¹⁷ The projection in Figure 7 elucidates that the maturation phase will be from 2021 with 100 publications and will reach the decline phase around 2040 (183 cumulative publications). According to the S-curve, in the next 5–10 years, there will be an increase in research and innovations related to applying bacteriophages in poultry farming systems.

FIG. 7.

S-curve for the number of publications over the years for the PHA list.

Figure 8 presents the modularization of the BAC list. Keywords, titles, and abstracts were organized in clusters and labeled in descending order according to their size, enhancing our understanding of how the topics are interconnected.

FIG. 8.

Keywords, titles, and abstracts organized in clusters for the BAC list.

The obtained clusters fit in the questions and insights of the present study, indicating not only the main bacteria responsible for infections but also a scientific concern related to the incidence of resistant microorganisms in poultry systems. Among the analyzed cluster, #0 campylobacter (158 members) and #5 Escherichia coli (36) were the predominant bacteria. Campylobacter species, mainly Campylobacter jejuni and C. coli, are highly prevalent in poultry farms and poultry products, being a significant source of human campylobacteriosis and a major cause of food-borne diseases.³³ E. coli or APEC, as discussed earlier, is responsible for poultry diseases (e.g., #3 colibacillosis), causing large losses in production systems. These two bacteria, together with Salmonella that did not appear among the clusters, possibly because it is generally asymptomatic and has higher levels of infection in eggs and meat, are the most worrying and have been focus of monitoring what justifies the #7 cluster label food safety;³⁴ Guard-Petter;³⁵ Chen et al.³⁶

Cluster #1, with 151 members, is related to the extended spectrum beta-lactamase enzymes (ESBL), a resistance mechanism expressed by bacteria prevalent in birds. The production of ESBL by pathogenic organisms is a challenge as it limits the use of broad-spectrum antibiotics widely used to prevent and treat avian diseases, justifying the cluster #8 tetracycline resistance.^37,38

The same grouping pattern was used for the PHA list, and Figure 9 represents the clusters obtained. The largest group, labeled field gel electrophoresis (#0), is a molecular technique to identify and profile bacteria that determines the existence of resistance genes.³⁹ The next cluster, named Escherichia coli (#1) and the Yersinia enterocolitica cluster (#4), depicts two predominant bacteria in poultry production systems.²³ The transmission route of Y. enterocolitica is fecal-oral, most often causing acute gastroenteritis with features of fever, vomiting, and diarrhea.⁴⁰ Reports indicate that yersiniosis was the third most reported food-borne illness in the European Union in 2015.⁴¹

FIG. 9.

Keywords, titles, and abstracts organized in clusters for the list PHA.

Chicken (3#), broiler chicken (#6), and antibiotics (#8) relate to the use of antibiotics in chicken production systems. Antibiotics such as tetracycline, bacitracin, tylosin, salinomycin, virginiamycin, and bambermycin are frequently used in intensive poultry farming, especially in North America.⁴² The use of these drugs in the poultry industry is carried out to improve meat production by increasing feed conversion, promoting growth rate, and preventing disease.³⁴ Applying subtherapeutic doses in poultry production promotes growth and protects bird health by modifying the immune status of broilers.⁴³ This is mainly due to controlling gastrointestinal infections and modifying the microbiota in the intestine.⁴⁴

Limitations

The 2,175 publications in list BAC and 97 in list PHA analyzed in this study constitute a significant portion of the research on the topic until 2022. However, this study has some limitations similar to any systematic review. The data used for analysis were obtained exclusively from the WoS database, which, although known worldwide and used for scientometric research, may have led to incomplete research. The research in WoS may not completely capture the most recent publications, as data from regulatory agencies and other languages were used in this work. However, the limitations do not detract from the merit of the work and provide a substantial overview of bacterial infections in poultry systems and the application of phages to combat them. Another aspect of this work is the quantitative nature of the literature review process. The analysis of keywords, prominent countries, citations, and other bibliographic data may not have the interpretative depth of traditional reviews. However, the data generated is the first in the literature to compare two lists on the topic, providing essential insights for understanding the state of the art.

Future Perspectives

The results are crucial to understanding bacterial infections in poultry systems and the potential application of bacteriophages to combat them. However, in the analyzed scenario, antimicrobial additives are still the most used and the practical application of bacteriophages in poultry systems needs to be studied in more depth.

The transition from a system that uses only antibiotics as a solution for bacterial infections to one that uses bacteriophages is not simple. Despite the emergence of this research topic, many challenges and gaps still need to be overcome to enable the application of bacteriophages. Few phage-based products are currently available or in the development phase to control infections in poultry systems. The development of phage cocktails capable of attacking multiple bacteria, phage carriers, and protection mechanisms, combined with increased in vivo testing, may be strategies to enable the technological application of phages in this sector.

Authors’ Contributions

H.C.R.: Conceptualization, formal analysis, and writing—original draft. G.V.S.: Investigation and writing—original draft. A.C.B.: Investigation and writing—original draft. N.D.C.G.: Writing—reviewing and editing conception, validation, and formal analysis. M.C.D.P.: Writing—reviewing and editing conception. N.C.G.: Conceptualization, writing—reviewing and editing conception, interpretation of data, and review.

Author Disclosure Statement

The authors report there are no competing interests to declare.

Funding Information

This work was financially supported by Coordination of Superior Level Staff Improvement and Fundação Araucária through the provision of scholarships. And by National Council for Scientific and Technological Development through concession projects: 309230/2021-7 and 422986/2021-6.