Antimicrobial resistance to colistin in neonates: epidemiological insights and public health implications in Nigeria – a mini review

Abstract

Introduction/Background

Antimicrobial resistance (AMR) remains a critical global health issue, particularly in low- and middle-income countries like Nigeria. Colistin, a last-resort antibiotic for multidrug-resistant Gram-negative infections, has seen rising resistance, posing a significant challenge for neonatal sepsis management. This narrative review focuses on colistin resistance in neonates in Nigeria, addressing a critical public health threat. With rising antimicrobial resistance, understanding its epidemiology in vulnerable populations is essential for effective interventions.

Methods

A narrative mini-review was conducted, focusing on literature, systematic reviews, and global and national reports on colistin resistance in neonates. Data were synthesized from studies across Africa, with an emphasis on epidemiological insights and implications for public health in Nigeria.

Results

The review identified an increasing trend of colistin resistance in Gram-negative bacteria in neonates across Nigeria. Key findings highlight the presence of mobile colistin resistance (MCR) genes, such as mcr-1, in clinical isolates from neonates, despite limited exposure to colistin. The analysis also emphasized the limitations in screening practices and gaps in neonatal AMR surveillance in Nigeria. The results suggest that inadequate antimicrobial stewardship, overuse of antibiotics, and poor healthcare infrastructure contribute to the rapid emergence of colistin resistance in neonates.

Conclusion

Colistin resistance in neonates poses a grave threat to public health. Addressing this issue requires urgent improvements in antimicrobial stewardship, neonatal care, and AMR surveillance systems. Strengthening laboratory capacities, improving infection prevention practices, and global cooperation are critical to mitigating the spread of colistin-resistant infections in neonates and reducing mortality in low-resource settings.

1. Introduction

Antimicrobial resistance (AMR), which occurs when bacteria, viruses, fungi, and parasites evolve and render drugs used to treat these infections less potent, remains this century’s most significant global health concern [1,2]. The human race has been in a perpetual battle with microbes. From bubonic plague, malaria, tuberculosis, human immunodeficiency virus, and recently, the COVID-19 pandemic. All of these resulted in numerous mortalities. Alexander Flemming’s discovery of penicillin earmarked the development of several antimicrobials, which tilted the battle with microbes towards the human race, previously the leading cause of death [3]. However, over the years, microbes continue to develop different resistance to antimicrobials, which has not only been worrisome but also has devastating consequences.

The effective use of antibiotics cuts across several ambits of modern medicine, including surgery, chemotherapy, organ transplantation, and, delicately, intensive care for preterm neonates [4]. Antibiotics have been used to reduce mortality and morbidity associated with infectious diseases [5]. Despite this, the inadequate use and overuse of antimicrobials in human medicine, veterinary medicine, agriculture, and pharmaceuticals in the environment have reduced the potency and efficacy of antimicrobial agents [6–8]. This situation is further compounded by the lack of newly developed antibiotics [4].

Global estimates show that the mortalities associated with bacterial AMR will be more than 1.27 million in 2019. If urgent and sustainable actions are not taken, it has been proposed that the mortality rate will increase to 10 million yearly by 2050 [9,10]. One in five of these deaths occurred among children under five years of age [11]. According to the systematic review that covers an extensive set of pathogens and pathogen–drug combinations, conducted by Murray et al. western sub-Saharan Africa has the highest number of all-age death rate attributable to bacterial AMR, at 27.3 deaths per 100 000 (20.9-35.3), while Australasia has the lowest at 6.5 deaths (4.3-9.4) per 100 000. The six leading ‘priority pathogens’ associated with bacterial AMR, Staphylococcus aureus, Klebsiella pneumoniae, Streptococcus pneumoniae, Acinetobacter baumannii, and Pseudomonas aeruginosa, were responsible for 929 000 (660 000–1 270 000) deaths attributable to AMR and 3·57 million (2·62–4·78) deaths associated with AMR in 2019 [1].

This extensive study highlights the disproportionately high burden of AMR in low-resource health systems, especially in western sub-Saharan Africa, including Nigeria. Lack of access to essential and effective antibiotics, challenges in implementing AMR surveillance programs, limited infrastructure and institutional capacity, reduced investment and human resources, inadequate information dissemination to regulatory bodies, and underutilization of available data have all been suggested to contribute to this level of burden [12–16]. An estimated 1·05 million deaths (95% UI 829 000–1 316 000) were associated with bacterial AMR and 250 000 deaths (192 000–325 000) were attributable to bacterial AMR in Africa in 2019 [15].

Seven leading pathogens were collectively responsible for 821 000 deaths (636 000–1 051 000) associated with resistance in this region, with four pathogens exceeding 100,000 deaths each: Streptococcus pneumoniae, Klebsiella pneumoniae, Escherichia coli, and Staphylococcus aureus. Third-generation cephalosporin-resistant K pneumoniae and meticillin-resistant S aureus were shown to be the leading pathogen–drug combinations in 25 and 16 countries, respectively (53% and 34% of the entire region, comprising 47 countries) for deaths attributable to AMR [15].

In Nigeria, 64,500 deaths were attributable to AMR and 263,400 deaths were associated with AMR. Sitting as the 185th highest age-standardized mortality rate per 100,000 people associated with AMR across 204 countries, the burden of bacterial AMR in Nigeria is disturbing [11]. In the context of other common health-related causes of death, deaths related to AMR in Nigeria are higher than deaths from respiratory infections, tuberculosis, cardiovascular diseases, maternal and neonatal disorders, enteric infections, neglected tropical diseases, and malaria. One can only imagine the devastating burden on the neonates.

Neonatal sepsis is one of the leading causes of neonatal death, especially in developing countries. Globally, there are 6.31 million incident cases of neonatal sepsis and 0.23 million deaths due to neonatal sepsis. Increasing trends in the incidence and decreasing trends in mortality of neonatal sepsis were observed worldwide from 1990 to 2019, with the highest absolute burden in sub-Saharan Africa and Asia [17]. According to the Burden of Antibiotic Resistance in Neonates from Developing Societies (BARNARDS) study, a prospective observational cohort study conducted by Milton et al. across 12 clinical sites including Nigeria, the incidence of clinically suspected sepsis was 166·0 (95% CI 97·69–234·24) per 1000 live births, laboratory-confirmed sepsis was 46·9 (19·04–74·79) per 1000 live births, and all-cause mortality was 0·83 (0·37–2·00) per 1000 neonate-days. The majority (881 [72·5%] of 1215) of laboratory-confirmed sepsis cases occurred within the first three days of life [18].

Neonates are most susceptible to infectious agents because of the immaturity of their immune systems [19]. Antibiotics are among the most commonly used drugs in neonatal intensive care units (NICU). This is unsurprising as neonatal sepsis presentations are often non-specific, and if nothing is done, it often results in disturbing consequences, including neurodevelopmental deficits and even death [20]. Consequently, empirical treatment is often provided. While the empirical use of antibiotics in neonates is not without adverse outcomes, bacterial AMR is associated with an increased mortality rate.

While gram-positive organisms, by virtue of their very nature, gram-positive organisms still have sensitivity to last line antibiotics, but gram-negative organisms have progressively developed resistance to an increasing number of antibiotics as can be seen in Figure 1 below. Carbapenemases have been found in increasing strains of Enterobacteriaceae, Pseudomonas aeruginosa and Acinetobacter baumannii, thus reducing the effectiveness of carbapenems [21]. Enterobacteriaceae (Escherichia coli, Enterobacter spp., and Klebsiella pneumonia) have developed resistance to third-generation cephalosporins via plasmid-mediated extended-spectrum β-lactamases (ESBLs) and AmpC β-lactamases(Singh et al. 2019 [22]) while rRNA region mutations have induced clarithromycin resistance in Helicobacter pylori [23]. This leaves tigecycline and colistin as medications of last resort against multi-resistant microorganisms.

Figure 1.

Classification of the world health organization priority list of antibiotic resistant bacteria.

Colistin was developed approximately fifty years ago and was among the first antibiotics to demonstrate significant activity against Gram-negative bacteria. Colistin exhibits a strong affinity for the lipid component of lipopolysaccharides and can selectively displace Mg²⁺ and Ca²⁺ from their cationic binding sites [24]. However, it was shelved due to concerns of neurotoxicity and, since then, has mostly been used in managing multidrug-resistant bacteria [25]. Despite having practically no clinical prescription in Nigeria, a study by Portal et al. in Northern Nigeria revealed that 1% of samples analyzing maternal and neonatal rectal microbiota were positive for at least one mobile colistin resistance (MCR) gene, which is the underlying cause of colistin resistance in Escherichia coli [26].

While the mechanisms of resistance to Colistin are still to be fully elucidated, the most common mechanism of resistance is via modifications to LPS, the initial site of action of Colistin, via modification of the lipid A with 4-amino-4-deoxy-L-arabinose (L-Ara4N) and phosphoethanolamine (PEtn), which in turn reduces the net LPS negative charge [25]. While it is an area of global health concern, social, political, and economic factors exacerbate the impact of AMR in low- and middle-income countries in comparison to high-income countries. For newborns who have immature immune systems, AMR can lead to severe infections with limited treatment options, resulting in high mortality rates. Addressing AMR in LMICs is critical to safeguarding the health of these populations. It requires strengthening healthcare systems, improving antibiotic stewardship, funding local research and development, and promoting global collaboration to develop effective solutions.

Antimicrobial resistance (AMR) to colistin in neonates is a growing public health concern, particularly in Nigeria, where neonatal infections contribute significantly to morbidity and mortality. Colistin, a last-resort antibiotic for multidrug-resistant infections, is increasingly compromised by resistance, threatening effective treatment options. This study aims to provide epidemiological insights into the prevalence, risk factors, and molecular mechanisms of colistin resistance in neonatal infections. Understanding these patterns will inform targeted interventions, antimicrobial stewardship, and policy formulation to mitigate resistance. Addressing colistin resistance is crucial for safeguarding neonatal health and strengthening Nigeria’s capacity to combat AMR in vulnerable populations.

The rest of this review is structured as follows: Section II provides an overview of Colistin, including the mechanism of action and role in treating multidrug resistance and sepsis in children; Section III details the emergence of colistin resistance in Nigeria; Section IV thoroughly discusses its impact on neonatal health, broader public health implications, and also highlights strategic responses and policy implications to mitigate its impact and spread.

2. Overview of colistin

Colistin is an antibiotic that combines lipophilic and hydrophilic properties, making it effective against Enterobacteriaceae and non-fermenter bacteria [27]. Colistin exhibits dual lipophilic and hydrophilic characteristics as a member of the polymyxin class of cationic polypeptides [28]. Although crucial for human medicine, Colistin’s long-term use in animal husbandry as a growth promoter has compromised its clinical effectiveness [27,29]. With the rise of multidrug-resistant Gram-negative bacilli, Colistin has been reintroduced as a last-resort treatment. However, resistance often arises due to mutations, some of which are plasmid mediated [27]. Colistin is notably effective against most Enterobacteriaceae, including Escherichia coli and Klebsiella pneumonia, as well as certain non-fermenter bacteria like Pseudomonas aeruginosa, except in organisms with intrinsic resistance [28]. The WHO has classified polymyxins as ‘Highest Priority Critically Important Antimicrobials for human medicine’, yet Colistin remains widely used in livestock for prophylaxis, therapy, and growth promotion [28]. Initially developed many years ago, Colistin (polymyxin) was withdrawn due to its nephrotoxicity and neurotoxicity. However, it is now used as a last line of defense against Gram-negative bacteria resistant to multiple drugs, including carbapenems [28]. As a last-resort agent, Colistin’s misuse and inadequate infection control in developing countries pose significant public health risks [30].

Colistin (polymyxin E) is a last-resort antimicrobial for treating life-threatening infections caused by multi-resistant enterobacteria. However, its use is now limited due to the rise of colistin-resistant bacteria [31]. The rise in antibiotic resistance among Gram-negative bacteria since the 1970s has escalated into a critical global issue [32]. The primary concern is the dwindling number of effective treatments for specific pathogens, particularly those responsible for hospital-acquired infections, which have the potential to spread widely, signaling a looming global health crisis [32]. Colistin was first introduced in the 1950s as an intravenous formulation and approved by the US FDA in 1959 for its bactericidal action against GNB, targeting infectious diarrhea and urinary tract infections. Polymyxins have been used for decades in topical treatments for eye and ear infections and selective bowel decontamination [32]. Challenges in antimicrobial susceptibility testing, dependence on broth dilution techniques, drug toxicity, insufficient pharmacokinetic-pharmacodynamic data, and poor clinical outcomes have all hindered the clinical use of Colistin [28,32].

2.1. Mechanism of resistance

Colistin resistance arises from either chromosomal mutations or the acquisition of transferable plasmids carrying mobile colistin resistance (MCR) genes. Chromosomal mutations involve alterations in one or more genes, such as pmrA, pmrB, mgrB, phoP, and phoQ in E. coli from livestock, contributing to lipid A biosynthesis changes in the outer membrane. This resistance mechanism can be passed vertically from generation to generation [31,32].

Conversely, plasmid-mediated colistin resistance can facilitate the horizontal transfer of resistance across different bacterial species or strains with varying virulence profiles. The MCR-1 gene, central to plasmid-mediated resistance, encodes a phospho-ethanolamine transferase that modifies lipid A by adding a phospho-ethanolamine group. This process reduces the negative charges on the lipopolysaccharide (LPS), diminishing its interaction with positively charged polymyxins [28,33,34]. Although the mcr-1 gene is most commonly found in E. coli, it is also present in other Enterobacteriaceae genera like Salmonella, Shigella, Klebsiella, and Enterobacter. This gene has been identified in several plasmid backbones (e.g. IncI2, IncHI2, IncP, IncX4, IncFI, and IncFIB), which are known for spreading antibiotic resistance genes among Enterobacteriaceae. The MCR-1 gene may also be mobilized alongside other mobile genetic elements, such as transposons and integrons carrying multidrug resistance determinants. Eight additional mcr genes (mcr-2 to mcr-10) have been identified [30,34]. The WHO Global Action Plan on Antimicrobial Resistance emphasizes research to enhance scientific understanding and support actions and investments addressing these issues [32,35]. Colistin primarily targets Gram-negative bacteria’s outer membrane (OM), specifically the LPS layer. The LPS comprises three domains: lipid A, the core oligosaccharide, and the O-antigen chain. Lipid A stabilizes the OM by anchoring the fatty acyl chains, while cations like Ca2+ and Mg2+ facilitate LPS molecule interactions, maintaining OM integrity [33,35]. The most recognized action of Colistin is through membrane lysis. Colistin interacts electrostatically with the phosphate groups of lipid A in the LPS, displacing Ca2+ and Mg2+ ions, destabilizing the OM, and integrating itself into the membrane, compromising its permeability. This disrupts the bacterial cell’s inner membrane, ultimately causing cell lysis [29,36]. Colistin also promotes vesicle–to–vesicle contact, facilitating phospholipid exchange between the OM and the inner leaflet of the cytoplasmic membrane, disrupting osmotic balance, and leading to cell death [37,38]. Additionally, Colistin generates reactive oxygen species (ROS), including hydroxyl radicals, through the Fenton reaction, causing oxidative damage to DNA, proteins, and lipids, ultimately resulting in bacterial death [32,37]. Furthermore, Colistin targets bacterial respiratory enzymes, specifically inhibiting the Type II NADH oxidoreductase in the inner membrane, impairing bacterial respiration and viability [28,36]. Lastly, Colistin exhibits anti-endotoxin activity by binding to lipid A in the LPS, neutralizing endotoxins, and mitigating infection-related inflammatory responses [30,34]. Despite advances in antimicrobial development, Colistin remains a critical last-resort option for treating multidrug-resistant and extensively drug-resistant Gram-negative bacteria. Due to their neutral charge at physiological pH, Colistin’s lower affinity for mammalian cell membranes partially accounts for its selective toxicity towards bacteria [31,35]. The mechanism by which Colistin exhibits synergy with other antimicrobials, such as β-lactams, gentamicin, rifampicin, meropenem, and tigecycline, involves its ability to destabilize the inner membrane of Gram-negative bacteria. This is achieved by incorporating hydrophilic groups into the fatty acid chains, disrupting membrane integrity, and leading to cell lysis. Colistin also binds to lipid A, exerting anti-endotoxin effects, preventing endotoxin-induced shock, and effectively solubilizing the bacterial cell membrane, resulting in a bactericidal effect [32,33,39].

Colistin resistance is a significant threat to global health, undermining the efficacy of one of the last-resort antibiotics used to treat multidrug-resistant Gram-negative bacterial infections. Resistance can develop through chromosomal mutations or the acquisition of plasmid-mediated mcr (mobilized colistin resistance) genes [34]. Chromosomal mutations typically modify the bacterial outer membrane by altering lipid A, a component of lipopolysaccharides, reducing colistin’s ability to bind and disrupt the membrane [40]. On the other hand, mcr genes, first discovered in Escherichia coli in 2015, allow resistance to spread rapidly through horizontal gene transfer, accelerating its dissemination across bacterial populations [41]. Colistin resistance has been identified in major pathogens such as Klebsiella pneumoniae, Pseudomonas aeruginosa, and Acinetobacter baumannii. The emergence of plasmid-mediated resistance is particularly alarming as it facilitates the transfer of resistance genes between species, compounding the challenge of controlling its spread. Resistant strains often show reduced susceptibility to other antibiotics, complicating treatment options. The increasing prevalence of colistin resistance highlights the urgent need for robust surveillance systems, restricted antibiotic use, and intensified research into alternative therapies. Without swift action, colistin resistance could render once-treatable infections virtually untreatable, posing a severe risk to public health [42].

Polymyxins, including colistin, are antibiotics often reserved as last-resort treatments for multidrug-resistant Gram-negative bacterial infections. In neonates, infections caused by carbapenem-resistant organisms necessitate the use of polymyxins [43]. However, the emergence of polymyxin resistance poses significant challenges in this vulnerable population. The mcr-1 gene, identified initially in China, confers plasmid-mediated resistance to colistin and has been detected in pathogens such as Escherichia coli and Klebsiella pneumonia [44]. Its presence in neonatal infections is concerning due to limited therapeutic alternatives. Risk factors for polymyxin-resistant infections include prior colistin treatment and prolonged hospitalization. In neonates, these factors, combined with underdeveloped immune systems, elevate the risk of acquiring such infections. The scarcity of data on polymyxin use in neonates underscores the need for pharmacokinetic and safety studies to establish optimal dosing and minimize toxicity. Additionally, novel antibiotics like cefiderocol have shown promise in treating multidrug-resistant Gram-negative infections in newborns, offering potential alternatives to polymyxins [45].

Understanding the molecular determinants of resistance to polymyxins may help develop suitable and effective methods for detecting polymyxin resistance determinants and the development of novel antimicrobial molecules [46]. Figure 2 below summarizes it visually.

Figure 2.

Mechanism of colistin resistance in neonates.

2.1.1. Role in treating multidrug-resistant infections and sepsis

The rise in antimicrobial resistance (AMR) among Gram-negative bacteria (GNB) presents a significant challenge in medical science due to their tendency to cause severe infections and rapidly develop resistance to antibiotics. This issue has been exacerbated by the misuse and overuse of antibiotics in both healthcare and agriculture, which has accelerated the spread of antibiotic-resistant strains [33,34,39]. Antibiotic resistance has been a growing issue for over fifty years and is now considered one of the twenty-first century’s most pressing public health challenges, particularly among GNB species [33]. With the dwindling number of effective antimicrobials available, there is renewed interest in the previously deprecated antibiotic, Colistin. Colistin has emerged as a last-resort therapy for multidrug-resistant (MDR) infections caused by Gram-negative bacteria. Although it was discontinued in the early 1980s due to nephrotoxicity and neurotoxicity, it is now being reconsidered as a critical resource for treating severely ill patients [35] However, certain Gram-negative pathogens, such as Brucella sp., Burkholderia cepacia, Helicobacter pylori, and others, typically do not show susceptibility to Colistin. Additionally, Campylobacter sp. exhibits a variable susceptibility range [35]. Despite these limitations, Colistin is used in critical conditions like bacteremia, sepsis, and ventilator-associated pneumonia (VAP) in intensive care units (ICUs). It is also considered an alternative treatment for other conditions, such as urinary tract infections, meningitis, osteomyelitis, and gastrointestinal infections [35].

2.2. Side effects

Colistin was previously avoided in clinical settings primarily due to its nephrotoxic effects, although this is less pronounced with the prodrug form, colistin sodium methanesulfonate. The nephrotoxicity is due to colistin’s re-absorption by proximal tubule cells through endocytosis and facilitated transport via human peptide transporter 2 (PEPT2) and carnitine/organic cation transporter 2 (OCTN2). This leads to mitochondrial and endoplasmic reticulum stress, resulting in cellular damage, lysis, and acute tubular necrosis [32,47].

Additionally, colistin may affect neuronal cells due to their high lipid content, with about 7% of patients experiencing neurological side effects such as paresthesia, seizures, confusion, ataxia, and visual disturbances. These effects are caused by a non-competitive presynaptic blockade of acetylcholine release, which can be reversed by discontinuing the therapy [32,47]. Patient characteristics such as age, sex, hyperbilirubinemia, hypoalbuminemia, underlying disease, and disease severity can also influence the side effects of colistin [27]. Renal damage from colistin is associated with increased tubular epithelial cell membrane permeability, leading to cell swelling and lysis [27]. Internal and external factors, including concurrent nephrotoxic drugs and various comorbid conditions, can exacerbate nephrotoxicity [27]. Colistin has shown synergistic activity when combined with ceftazidime, rifampicin, and amikacin, particularly for infections caused by multidrug-resistant Pseudomonas aeruginosa [28,33]. Therapeutic drug monitoring is crucial due to colistin’s variable pharmacokinetics and narrow therapeutic window, which complicates treatment management and emphasizes the need for practical and rapid drug monitoring methods [33]. Awareness of colistin’s risk factors and preventive measures is essential for minimizing morbidity and mortality while ensuring effective therapy with reduced risks [35]. Since its reintroduction in China in 2018, colistin sulfate has increasingly been critical in treating carbapenem-resistant organisms (CROs) [36]. The efficacy of colistin sulfate and its combinations with other antimicrobials is influenced by the treatment course and the low incidence of nephrotoxicity and neurotoxicity, which provides valuable guidance for its rational clinical use [36]. Oxidative stress contributes to colistin-induced renal damage, marked by elevated renal MDA, decreased GSH levels, and increased serum BUN and creatinine levels [37]. Renal function at the end of colistin treatment depends on baseline renal function and the occurrence of shock [38]. As a cationic polypeptide antibiotic, colistin disrupts the outer membrane of Gram-negative bacteria, leading to bacterial death. It is administered as colistin sulfomethate sodium and excreted by glomerular filtration [39].

Colistin remains effective in vitro against most strains of Pseudomonas aeruginosa, Klebsiella pneumoniae, Acinetobacter spp., and Enterobacter spp. However, resistance is common in Proteus spp., Providencia spp., Serratia spp., and some Stenotrophomonas maltophilia strains [39]. Its moderate incidence of complications suggests it may be a relatively safe option for patients with normal renal function when administered with proper monitoring in an ICU [39]. Intravenous colistin should be considered for severe Gram-negative infections when it is the only effective antibiotic in vitro [39].

3. Emergence of colistin resistance in Nigeria

3.1. Discovery and reporting

There is a paucity of data to narrate colistin resistance among Nigerian newborns. This could be attributed to the scarcity of screening for colistin resistance in humans. Most of the screenings for colistin resistance were carried out in animals. Colistin resistance gene mcr was first discovered in 2016 among pigs in China [26]. In 2016, colistin resistance gene mcr-1 was reported in South Africa among broiler chickens [48]. In Southern Nigeria, an investigation was carried out, and 2.9% of colistin resistance gene mcr-1 was reported [49].

A recent retrospective study carried out in pregnant women and newborns from three clinical sites in Nigeria (two in Abuja and one in Kano) screened for colistin resistance mcr gene. 963 rectal swabs were collected from babies. Screening was carried out by polymerase chain reaction (PCR) to detect mcr-1, mcr-3, and mcr-8-10. 8 distinct bacteria isolates were discovered. The prevalence of mcr carriage was reported to be 0.7% in neonates (newborns). It is not certain where the resistance came from as neither the mothers nor the newborns were prescribed colistin. 7 neonatal sepsis was reported, and 3 had blood culture confirmation of the causative microbes. Enterobacter gotten from the rectum of the neonates was not the cause of the sepsis. These newborns with sepsis were treated with either amoxicillin and ceftazidime or amoxicillin and gentamicin. The following species of bacteria were discovered in both pregnant women and newborns: Enterobacter cloacae, Enterobacter kobei, Enterobacter asburiae, Enterobacter roggenkampii, Enterobacter spp, shigella, Escherichia coli, Klebsiella quasipneumonia. Out of the 8 bacterial isolates recovered from the neonatal rectal swabs, 7 isolates were Enterobacter species, and they all carried mcr-10 genes [26]. Portal et al. employed a Broth-based test, Polymerase Chain Reaction, Whole Genome Sequencing and Bioinformatics analysis for this cohort study.

There are not enough research publications to discuss colistin resistance among newborns in Nigeria further. Further primary research needs to be carried out to investigate colistin resistance in neonates, including newborns whose mothers have positive HIV status. Also, the research done by these authors focused on just two states in Nigeria (Abuja and Kano); further research in other parts of Nigeria is encouraged [26].

3.2. Detection methods for colistin resistance

Colistin-resistant detection methods can be divided into phenotypic and molecular methods, as shown in Figure 3 below [34,50].

Figure 3.

Image showing the different detection methods for colistin resistance.

3.2.1. Rapid polymyxin NP (nordmann/poirel) test

The test detects fermentation of glucose associated with bacterial growth in the presence of a defined concentration of polymyxin E or B. The presence of an acid metabolite is noted by a change in PH and the indicator (red phenol) colour from orange to yellow. This test has a sensitivity and specificity of 99.3% and 95.4%, respectively [51].

3.2.2. Broth-based test

This is jointly recommended by the Clinical and Laboratory Standards Institute (CLSI) and European Committee on Antimicrobial Susceptibility Testing (EUCAST) guidelines as the gold standard for colistin resistance detection. It involves preparing a series of two-fold dilutions of colistin sulfate in polysorbates, followed by the addition of bacterial inoculum and incubation at 370 C for 18 h. If no bacterial growth is observed in the concentration, it is regarded as the minimal inhibitory concentration (MIC). According to EUCAST, the breakpoint for colistin is at 2 mg l _1 (susceptible) and 2 mg l _1 (resistant). CLSI has removed the susceptible category. A broth-based test involves the preparation of different dilutions of antibiotics. Hence, it is only routinely carried out in some labs [52].

3.2.3. Chromogenic media

The first agar medium for detecting colistin-resistant Gram-negative rods, Super Polymyxin, is used for detecting colistin-resistant Enterobacter strains, including those with low MIC values that harbour the mcr-1 gene. It comprises eosin methylene blue (EMB) agar, colistin, daptomycin, and amphotericin B (3.5, 10, and 5 µg/ml, respectively). A second colistin-resistant detecting medium is CHROMagar COL-APSE, incorporating colistin sulfate and oxazolidinone antibiotics. Its advantage over SuperPolyxin medium is that it can differentiate colistin-resistant Enterobacterial strains from non-fermenting rods. Another medium, Lucie-Bardet-Jean-Marc-Rolain (LBJMR), is a polyvalent culture medium for isolating and selecting colistin-resistant and vancomycin-resistant bacteria. The LBJMR medium was developed with the addition of colistin sulphate salt (4 µg/ml), vancomycin (50 µg/ml), and a substrate for fermentation (7.5 g/l of glucose) to a Purple Agar Base (31 g/l). In 2018, CHROMID Colistin R agar came into the market, and it is used for screening colistin-resistant Enterobacteriaceae in clinical samples, such as stools and rectal swabs. The CHROMID Colistin R is a quantitative diagnostic test that differentiates colistin-resistant isolates from susceptible ones [34,50,51,53].

3.2.4. EDTA-based assays (CDT, CMR, MRPNP, and alteration of Zeta potential)

Four EDTA-based assays were designed to detect mcr-positive E. coli isolates, which was evaluated using 109 Enterobacteriaceae isolates from humans, animals, and food. The four EDTAs (CDT, CMR, MRPNP, and alteration of Zeta potential) are based on the chelation of zinc ions, which are required for the enzymatic activity of the phosphoethanolamine transferase, mcr-1. Inhibiting the zinc role in E. coli reduces colistin’s MIC value, hence underscoring the zinc’s role [50,53,54]. Table 1 below is the sensitivity and specificity of each EDTA based assay [50].

Table 1.

Showing the sensitivity (%) and specificity (%) of each EDTA based assay.

EDTA (ethylenediaminetetra-acetic acid) assay	Sensitivity (%)	Specificity (%)	Remark
CDT (Combined Disk Test)	96.7	89.6	Less efficient, although more recommendable than CMR
CMR (Colistin MIC Reduction)	96.7	83.3	Less efficient than CDT
MRPNP (Modified rapid polymyxin Nordmann Poirel)	96.7	100	Better than CDT and CMT
Alteration of Zeta Potential	95.1	100	Second to MRPNP in terms of efficiency

3.2.5. Polymerase chain reaction (PCR) – based assay

PCR rapidly detects MCR genes. A real-time PCR technique can detect mcr-1 and mcr-2 genes in E. coli isolated from cecal and faecal samples. Block multiplex PCR was developed as a rapid way to detect different mcr genes (mcr 1- 5 genes) [34].

3.2.6. Whole Genome Sequencing (WGS)

WGR is used to detect the presence of plasmid-mediated resistance genes. Softwares like PlasmidFinder can be used to identify plasmid replicons from WGS data. WGS can be used to identify the mcr-1 gene, which is the first plasmid-mediated gene granting colistin resistance [34,52].

3.2.7. Loop-Mediated isothermal amplification (LAMP)

This technique is used to amplify nucleic acids under static temperature conditions. It is a rapid and specific technique because it can produce 109 copies of target genes. LAMP makes use of Bst DNA polymerase to produce DNA through strand displacement. A single LAMP assay can detect the MCR-1 gene in Enterobacteriaceae isolates, assessing results through chromogenic visualization and real-time turbidity monitoring. Multiplex LAMP was invented for mcr-1 to mcr-5 genes with 100% sensitivity and specificity. Multiplex LAMP utilizes restriction endonucleases to detect mcr-1-5 genes [34,50,52].

3.2.8. Microarray

In 2017, Bernasconi et al. evaluated a new commercial microarray that can simultaneously detect both -lactamases and mcr-1/mcr-2 genes from bacterial cultures. The CT103XL microarray uses a multiple-ligation detection reaction to identify all isolates expressing ESBLs, mcr-1 and mcr-2 genes, including other variants such as mcr-1.1, mcr-1.2, mcr-1.3, mcr-1.4, upto mcr-1.7 in a space of 6.5 h. It has a sensitivity and specificity of 100%. The CT103XL microarray could not detect the mcr-3 gene, which has a 45% and 47% sequence homology to mcr-1 and mcr-2, respectively [34,50].

3.2.9. Klebsiella Pneumonia Isolates detection

The three typing techniques for detecting K. pneumonia operons are Ribotyping, Multilocus Sequence Typing (MLST) and Infrared Biotyping (IRBT). K. pneumonia has eight highly conserved operons, 23S and 16 rRNA, on the chromosomes. Restriction enzymes may accurately cut these operons to produce restriction pattern bands that assist in differentiation, analysis and interpretation. Ribotyping has proven to be a powerful typing method, capable of overcoming the limitations often found in traditional methods, such as insufficient typeability and reproducibility. MLST is a generally used DNA sequence-based method for molecular characterization and assessing the genetic relatedness of various bacterial genera. Recently, a homologous analysis of clinical isolates of enteral and extraintestinal K. pneumoniae in China using MLST revealed six sequence categories, all classified as ST5235. IRST is a promising technique for typing bacterial strains, especially in the context of hospital hygiene management. The study aimed to establish cutoff value limits and standardize culture procedures for typing K. pneumoniae isolates using the IR Biotyper (IRBT) method. IRBT has proven to be a highly effective method for typing bacterial strains, enabling reliable and timely investigations into hospital outbreaks [34].

4. Implications for neonatal and global public health

The emergence of AMR to Colistin in newborns severely affects the clinical management of infections. AMR increases the difficulties in selecting effective antimicrobial treatments for the affected infant and limits the choice of alternative antibiotics [55]. Colistin is usually a substitute treatment for AMR for other medications. Hence, colistin-resistant infections would result in fewer treatment options, reduced effectiveness, or increased toxicity. AMR is dangerous, especially during sepsis, where survival is heavily reliant on administering effective treatment early [56]. Studies indicate that failure to control infections due to AMR can contribute to rapid health decline and lead to increased infant morbidity and mortality rates [55,57]. However, the dependence on alternative antibiotics like carbapenems or cephalosporin may increase the risk of adverse effects. Carbapenems are associated with nephrotoxicity, which can be fatal among newborns whose kidneys are developing [58,59]. Cephalosporins are associated with hypersensitivity or allergic reactions, and this is particularly harmful in neonates [60]. Furthermore, colistin-resistant infections usually require more extended hospitalization. Prolonged hospitalization leads to increased healthcare costs and exposes newborns to hospital-acquired infections (HAIs), which complicates AMR management [61,62]. The susceptibility to HAIs complicates the immediate health implications for neonates, increases the risk of poor treatment outcomes and increases mortality [61,62]. Colistin resistance can lead to resistance in other antimicrobial medications, known as cross-resistance, which further limits treatment options available to combat various infections [63,64].

Beyond the immediate implications of AMR to Colistin, it also poses neonatal health problems and public health concerns. Due to the persistence and severity of the infections, infants who recover from colistin-resistant infections may develop chronic health complications such as neurodevelopmental delays, chronic lung disease, renal diseases, and other health challenges [65,66]. These chronic diseases also affect the quality of life of newborns, spanning into adulthood.

From a public health standpoint, colistin resistance is concerning because these strains can spread beyond newborns. Although usually spread from mother to child [26,67], it could also spread into the broader population, increasing the prevalence of AMR strains. These strains may also spread internationally, contributing to the global burden of AMR and complicating infection management worldwide. In LMICs like Nigeria, where healthcare systems are overburdened, the long-term implications on these systems are dire. The need for more intensive care and the utilization of more expensive or less available antibiotic alternatives may overload the existing healthcare systems and the ability to manage infections and their spread effectively [62,68,69].

The prevalence of Colistin-resistant infections reveals a need for better AMR surveillance and infection management. Effective surveillance supports early detection of AMR infections, which helps contain infection and prevents the spread of resistant strains within healthcare settings and communities. Surveillance of AMR aids healthcare systems in reporting drug-resistant infections and to better understand the spread of AMR [70,71]. However, many LMICs need the necessary resources and infrastructures to conduct proper AMR surveillance, which hinders early interventions. Poor health system governance, lack of health system information, lack of laboratory infrastructures, limited staff and inadequate experience and expertise hinder proper surveillance in LMICs [70]. Healthcare systems must be developed to ensure proper staffing, high-standard laboratories, and health system governance to manage AMR effectively and ensure more robust surveillance of AMR infections. There is also a need to strengthen infection management practices and halt the spread of colistin-resistant infections. Such practices include proper WASH facilities, adherence to hand hygiene protocols, provision and utilization of personal protective equipment (PPE) and antibiotics sensitization programs to reduce the unnecessary use of broad-spectrum antibiotics [72,73]. These measures must be adequately enforced in neonatal intensive care units (NICUs) to protect vulnerable neonates.

5. Conclusion

This study provides a comprehensive analysis of the escalating challenge posed by Colistin-resistant bacteria, underscoring the profound implications for global public health. The findings reveal a disturbing trend of increasing resistance, driven by both the horizontal gene transfer of the mcr-1 gene and other adaptive mechanisms. This trend is particularly concerning given Colistin’s role as a critical last-line antibiotic for treating infections caused by multidrug-resistant organisms. The misuse and overuse of Colistin in clinical settings and agricultural practices have been identified as key drivers of this resistance, highlighting the urgent need for improved stewardship and regulatory oversight. The spread of Colistin resistance not only compromises current treatment protocols but also threatens to render obsolete one of the few remaining therapeutic options for severe infections.

Finally, this study emphasizes the necessity for robust global surveillance networks to track the dissemination of resistance genes and the need for ongoing research into alternative antimicrobial therapies. These efforts must be complemented by international cooperation to enforce stricter guidelines on antibiotic use and to promote the development of new drugs and treatment strategies.

Funding Statement

The author(s) reported there is no funding associated with the work featured in this article.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

Data sharing is not applicable to this study as no new data was created or analyzed.