Microbial Contamination of Chicken Litter Manure and Antimicrobial Resistance Threat in an Urban Area Setting in Cameroon

Prevalence and Serotype of Poultry Salmonellosis in Africa: a Systemic Review and Meta-Analysis

Salmonellosis represents a significant economic and public health concern for the poultry industry in Africa, leading to substantial economic losses due to mortality, reduced productivity, and food safety problems. However, comprehensive information on the burden of poultry salmonellosis at the continental level are scarce. To address this gap, a systemic review and meta-analysis were conducted to consolidate information on the prevalence and circulating serotypes of poultry salmonellosis in African countries. This involved the selection and review of 130 articles published between 1984 and 2021. A detailed systematic review protocol was structured according to Cochrane STROBE and PRISMA statement guidelines. From the 130 selected articles from 23 different African countries, the overall pooled prevalence estimate (PPE) of poultry salmonellosis in Africa was found to be 14.4% (95% CI= 0.145-0.151). Cameroon reported the highest PPE at 71.9%, with the country also noting the highest specific prevalence of 93.3%. The PPE was notably high in meat and meat products at 23%, indicating significant contamination of Salmonella in African poultry meat and meat products. The number of research papers reporting poultry salmonellosis in Africa has been a threefold increase from 1984 to 2021. Salmonella Enteritidis and Typhimurium were the two most prevalent serotypes reported in 18 African countries. Besides, Salmonella Kentucky, Virchow, Gallinarum, and Pullorum were also widely reported. Western Africa had the highest diversity of reported Salmonella serotypes (141), in contrast to southern Africa, which reported only 27 different serotypes. In conclusion, poultry salmonellosis is highly prevalent across Africa, with a variety of known serotypes circulating throughout the continent. Consequently, it is crucial to implement strategic plans for the prevention and control of Salmonella in Africa.

Isolation and molecular characterization of multidrug‑resistant Escherichia coli from chicken meat

Antibiotics in animal farms play a significant role in the proliferation and spread of antibiotic-resistant genes (ARGs) and antibiotic-resistant bacteria (ARB). The dissemination of antibiotic resistance from animal facilities to the nearby environment has become an emerging concern. The present study was focused on the isolation and molecular identification of Escherichia coli (E. coli) isolates from broiler chicken meat and further access their antibiotic-resistant profile against different antibiotics. Broiler chicken meat samples were collected from 44 retail poultry slaughter shops in Prayagraj district, Uttar Pradesh, India. Standard bacteriological protocols were followed to first isolate the E. coli, and molecular characterization was performed with genus-specific PCR. Phenotypic and genotypic antibiotic-resistant profiles of all confirmed 154 E. coli isolates were screened against 09 antibiotics using the disc diffusion and PCR-based method for selected resistance genes. In antibiotic sensitivity testing, the isolates have shown maximum resistance potential against tetracycline (78%), ciprofloxacin (57.8%), trimethoprim (54.00%) and erythromycin (49.35%). E. coli bacterial isolates have shown relative resistant to amoxicillin-clavulanic acid (43.00%) and against ampicillin (44.15%). Notably, 64.28% E. coli bacteria were found to be multidrug resistant. The results of PCR assays exposed that tetA and blaTEM genes were the most abundant genes harboured by 83 (84.0%) and 82 (82.0%) out of all 99 targeted E. coli isolates, followed by 48.0% for AmpC (CITM) gene and cmlA (23.00%) for chloramphenicol resistance. It is notable that most of the isolates collected from chicken meat samples were multidrug resistant (> 3 antibiotics), with more than 80% of them carrying tetracycline (tetA) and beta-lactam gene (blaTEM). This study highlights the high risk associated with poultry products due to MDR-E. coli and promote the limited use of antibiotics in poultry farms.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-024-03950-7.

Antimicrobial susceptibility testing data analysis over 3 years at the Yaoundé General Hospital, Cameroon

Background

Antimicrobial resistance (AMR) is a major health concern with high rates in low-income countries. Bacteriology laboratories sustain the fight against AMR by providing antibiotic susceptibility testing (AST) results to ensure appropriate therapies. These laboratories generate a lot of data, which are usually used for prospective interventions. Our study conducted in a lower-middle-income hospital setting aimed to describe the profile of bacteria isolated from the specimens received over 3 years, assess their susceptibility profile and identify potential gaps or area of improvement from the analysis of our data.

Methods

Monthly data were retrieved from registers for all specimens received between January 2020 until December 2022. Data were compiled and analysed using the R and WHONET software.

Results

Out of 3582 specimens received, 797 were culture positive (22.3%). Escherichia coli and Klebsiella pneumoniae were frequently isolated (30.5% and 24.2%, respectively). AST results analysis showed high resistance of Gram-negative bacteria to penams and cephems, whereas low resistance was observed to carbapenems. Susceptibility to antibiotics based on the AWaRe antibiotic classification was variable. The bacteriological profile in the various types of specimen was established and rational information to design a therapeutic protocol adapted to our hospital setting was obtained.

Conclusions

AST results may not only be used for prospective guidance for treatment, but rather cumulative data analysis can contribute to design effective antibiotic prescriptions and improve general practices at the laboratory. This is, however, dependent on a good record-keeping, standardization of practices and collaboration between clinicians and laboratory scientists.

Hazards Associated with the Combined Application of Fungicides and Poultry Litter in Agricultural Areas

In recent decades, the poultry farming industry has assumed a pivotal role in meeting the global demand for affordable animal proteins. While poultry farming makes a substantial contribution to food security and nutrition, it also presents environmental and public health challenges. The use of poultry litter as fertilizer for agricultural soils raises concerns about the transfer of pathogens and drug-resistant microorganisms from poultry farms to crop production areas. On the other hand, according to the Food and Agriculture Organization of the United Nations (FAO), fungicides represent the second most used chemical group in agricultural practices. In this context, agricultural soils receive the application of both poultry litter as a fertilizer and fungicides used in agricultural production. This practice can result in fungal contamination of the soil and the development of antifungal resistance. This article explores the necessity of monitoring antifungal resistance, particularly in food production areas with co-application of poultry litter and fungicides. It also highlights the role of fungi in ecosystems, decomposition, and mutualistic plant associations. We call for interdisciplinary research to comprehensively understand fungal resistance to fungicides in the environment. This approach seeks to promote sustainability in the realms of human health, agriculture, and the environment, aligning seamlessly with the One Health concept.

A snapshot survey of antimicrobial resistance in food-animals in low and middle-income countries

Antimicrobial resistance remains a threat to global public health. Low-and middle-income countries carry a greater burden of resistance because of higher rates of infection as well as, potentially, location-specific risk factors. Food animals occupy a critical crossover point for the spread of antimicrobial resistance to humans and the environment. However, this domain remains poorly surveilled outside high-income settings. We used point surveillance from 191 studies reporting phenotypic AMR in food animals across 38 African, Middle Eastern, Asian and South and Central American countries to depict antimicrobial resistance trend in food animals. By computing Multiple Antibiotic Resistance indices and finding an overall mean of 0.34 ± 0.16, which is above the 0.2 index associated with multidrug resistance and high risk, we show that multidrug resistance in bacteria from food animal sources is worryingly high. MAR indexes from food animals were overall higher than those previously computed from aquaculture but, unlike aquaculture-computed MAR indices, did not track closely with those of human-associated bacteria in the same countries. Food animals are an important reservoir for rising antimicrobial resistance in bacteria, and hence improved surveillance in this sector is highly recommended.

Application of Eugenol in Poultry to Control Salmonella Colonization and Spread

The poultry sector is an essential component of agriculture that has experienced unprecedented growth during the last few decades. It is especially true for the United States, where the average intake of chicken meat increased from 10 pounds (4.5 kg) per person in 1940 to 65.2 pounds (29.6 kg) per person in 2018, while the country produced 113 billion eggs in 2019 alone. Besides providing nutrition and contributing significantly to the economy, chicken is also a natural reservoir of Salmonella, which is responsible for salmonellosis in humans, one of the significant foodborne illnesses around the globe. The increasing use of chicken manure and antibiotics increases the spread of Salmonella and selects for multi-drug resistant strains. Various plant extracts, primarily essential oils, have been investigated for their antimicrobial activities. The multiple ways through which these plant-derived compounds exert their antimicrobial effects make the development of resistance against them unlikely. Eugenol, an aromatic oil primarily found in clove and cinnamon, has shown antimicrobial activities against various pathogenic bacteria. A few reports have also highlighted the anti-Salmonella effects of eugenol in chicken, especially in reducing the colonization by Salmonella Enteritidis and Salmonella Typhimurium, the primary Salmonella species responsible for human salmonellosis. Besides limiting Salmonella infection in chicken, the supplementation of eugenol also significantly improves intestinal health, improving overall well-being. In this review, we highlight the rising incidences of salmonellosis worldwide and the factors increasing its prevalence. We then propose the usage of eugenol as a natural feed supplement for containing Salmonella in chicken.

Microbial Contamination of Bedding Material: One Health in Poultry Production

In poultry farms, the mixture of bedding material, chicken excrement, and feathers seems to play an important role in pathogen development which may contribute to a potential risk of zoonosis, spreading the disease through the food chain. The purpose of this study was to analyze microbial contamination in bedding material and other matrices as well as potential antimicrobial resistances in chicken production facilities, and also to identify the sampling techniques and assays used. This study evidences the available data published, following the PRISMA methodology. Among the environmental samples, surface swabs were frequently used as a passive sampling technique. Morphological identification was performed in all studies. From all the matrices, the bedding material was the most contaminated. Most studies focused on bacterial contamination, with Salmonella sp. and Campylobacter sp. being commonly reported and three studies evidenced fungal contamination, being Penicillium sp.- and Aspergillus sp.-dominant. Mycotoxin assessment was only performed in one study, being identified in all bedding samples. The screening for bacteria resistance evidenced bacteria multidrug resistance; however, fungal susceptibility to azoles was not assessed in any of the analyzed studies. Briefly, this review evidences the microbial contamination in poultry facilities, emphasizing animals' bedding as a potential source of contamination. Additionally, this study contributes to a sampling and analysis protocol proposal to assess the microbial contamination in this setting. Additionally, the knowledge gaps identified highlight the need of further research regarding microbial contamination and toxicological potential on animals' bedding in order to mitigate the exposure in poultry pavilions.

Antibiotic resistomes and their chemical residues in aquatic environments in Africa

The aquatic environment is a hotspot for the transfer of antibiotic resistance to humans and animals. Several reviews have put together research efforts on the presence and distribution of antibiotic resistant bacteria (ARB), antibiotic resistance genes (ARGs), and antibiotic chemical residue (ACRs) in food, hospital wastewater, and even in other aquatic environments. However, these reports are largely focused on data from developed countries, while data from developing countries and especially those in Africa, are only marginally discussed. This review is the first effort that distills information on the presence and distribution of ARGs and ACRs in the African aquatic environments (2012-2021). This review provides critical information on efforts put into the study of ARB, ARGs, and ACRs in aquatic environments in Africa through the lens of the different sub-regions in the continent. The picture provided is compared with those from some other continents in the world. It turns out that the large economies in Africa (South Africa, Nigeria, Tunisia, Kenya) all have a few reports of ARB and ARGs in their aquatic environment while smaller economies in the continent could barely provide reports of these in their aquatic environment (in most cases no report was found) even though they have some reports on resistomes from clinical studies. Interestingly, the frequency of these reports of ARB and ARGs in aquatic environments in Africa suggests that the continent is ahead of the South American continent but behind Europe and Asia in relation to providing information on these contaminants. Common ARGs found in African aquatic environment encode resistance to sulfonamide, tetracycline, β-lactam, and macrolide classes of antibiotics. The efforts and studies from African scientists in eliminating ARB and ARGs from the aquatic environment in Africa are also highlighted. Overall, this document is a ready source of credible information for scientists, policy makers, governments, and regional bodies on ARB, ARGs, and ACRs in aquatic environments in Africa. Hopefully, the information provided in this review will inspire some necessary responses from all stakeholders in the water quality sector in Africa to put in more effort into providing more scientific evidence of the presence of ARB, ARGs, and ACRs in their aquatic environment and seek more efficient ways to handle them to curtail the spread of antibiotic resistance among the population in the continent. This will in turn, put the continent on the right path to meeting the United Nations Sustainable Development Goals #3 and #6, which at the moment, appears to be largely missed by most countries in the continent.

Molecular mechanisms and clonal lineages of colistin-resistant bacteria across the African continent: A scoping review

Colistin (also known as Polymyxin E), a polymyxin antibiotic discovered in the late 1940s, has recently reemerged as a last-line treatment option for multidrug-resistant infections. However, in recent years, colistin-resistant pathogenic bacteria have been increasingly reported worldwide. Accordingly, the presented review was undertaken to identify, integrate and synthesize current information regarding the detection and transmission of colistin-resistant bacteria across the African continent, in addition to elucidating their molecular mechanisms of resistance. PubMed, Google Scholar, and Science Direct were employed for study identification, screening and extraction. Overall, based on the developed literature review protocol and associated inclusion/exclusion criteria, 80 studies published between 2000 and 2021 were included comprising varying bacterial species and hosts. Numerous mechanisms of colistin resistance were reported, including chromosomal mutation(s) and transferable plasmid-mediated colistin resistance (encoded by mcr genes). Perhaps unexpectedly, mcr-variants have exhibited rapid emergence and spread across most African regions. The genetic variant mcr-1 is predominant in humans, animals, and the natural environment, and is primarily carried by IncHI2- type plasmid. The highest numbers of studies reporting the dissemination of colistin-resistant Gram-negative bacteria were conducted in the North African region.

Antibiotic Resistance of Bacterial Isolates from Smallholder Poultry Droppings in the Guinea Savanna Zone of Nigeria

There is a growing risk of antibiotic resistance (AR) in smallholder poultry (SP). This study, therefore, aimed to investigate AR pattern of bacterial isolates from SP in the Guinea Savanna agro-ecological zone of Nigeria. A total of 120 fresh poultry droppings were aseptically collected, randomly, from two tropically adapted (FUNAAB Alpha and Noiler) and local chickens. The chickens were raised either using ethnoveterinary medicines (n = 60) or antibiotics (n = 60). Bacterial isolates were characterized and analyzed using standard protocols, and appropriate statistical tools. Compared to Pseudomonas spp. (2.5%) and Klebsiella spp. (5.8%), Salmonella spp. (57.5%) and Escherichia coli (34.2%) were the most prevalent (χ2 = 96.67; p < 0.001). Prevalence of bacterial species was significantly (p = 0.024; Odds Ratio = 2.552) influenced by antibiotics usage. All four species were multi-drug resistant. In total, 30% of the isolates had a multiple AR index ≥ 0.2. Bacterial isolates from FUNAAB Alpha (58.0%) and Noiler (44.0%) were highly resistant to quinolones, while isolates from the local chickens (22.6%) were most resistant to aminoglycosides. Bacterial species isolated from FUNAAB Alpha and local chickens exhibited the lowest and highest percentage of AR, respectively. Clustering of isolates with similar antibiogram revealed inter-species dependence with possibility for inter-species gene transfer. These findings provide a background to investigate the metagenomics of local and improved chickens for AR.

An assessment of knowledge and attitude toward antibiotic misuse by small-scale broiler farmers in Bogor, West Java, Indonesia

Background and Aim:

Antibiotics are often overused and misused by broiler farmers. Moreover, this practice may lead to antibiotic resistance. Antibiotics may be used for various purposes such as therapy, prophylaxis, flushing, and growth promoters. The study aimed to examine the association of knowledge and attitudes with antibiotics used by broiler farmers.

Materials and Methods:

The study design was cross-sectional. The data were obtained from interviewing 132 farmers’ households in Bogor District, West Java, Indonesia. The outcome variable was antibiotic use, whereas the independent variables included knowledge and attitude toward antibiotic resistance. The statistical analysis used a t-test and correlation test.

Results:

A total of 78% of broilers farmers use antibiotics, and most of the farmers used antibiotics for flushing and prophylaxis. Furthermore, antibiotic use was associated with broiler farmers’ knowledge and attitudes toward antibiotic resistance. However, there is no significant correlation between the duration of antibiotics use and their knowledge and attitude.

Conclusion:

The use of antibiotics in broilers is still high in Bogor, and most of the used antibiotics belong to the Medically Important Antimicrobial category. In general, the use of antibiotics in broilers is influenced by knowledge.

Status of disease prevalence, drugs and antibiotics usage in pond-based aquaculture at Narsingdi district, Bangladesh: A major public health concern and strategic appraisal for mitigation

This research aimed to investigate the present status of disease prevalence and usage of aqua drugs for various aquaculture operations in the Narsingdi region of Bangladesh. Data were collected through the market survey, preset questionnaire interview, personal contact, and participatory rural appraisal tools. Amongst the respondents, the maximum percentages were found practicing mixed cultures of carp, tilapia, and pangas. The respondents suggested that epizootic ulcerative syndrome, saprolegniasis, streptococcosis, tail and fin rot and bacillary necrosis are common fish diseases in the area. About 140 drugs of different companies used in aquaculture for different purposes such as disease treatment, growth enhancement, water quality improvement, toxic gas removal, improvement of feed conversion ratio. Zeolite, rotenone, disinfectant, oxygen precursors, ammonia reducers, and probiotics were applied for pond preparation, water, and soil quality maintenance, while 30 different antibiotics were used for the purpose of treatment. Among the available antibiotics, oxytetracycline, ciprofloxacin, enrofloxacin, erythromycin, sulphadiazine, and trimethoprim were found extensively used by the fish farmers. Four enzymes and eighteen growth promoters were identified as being utilized to enhance digestion and boost up the production. This study elicited various issues connected with application and administration of such aqua chemicals, including farmers’ ignorance about their usage, proper doses, application methods, withdrawal period, and the human health concerns associated with their irresponsible use. However, the consequences of these chemical products to the environment, animal health, and human health required further study for the betterment of mankind.

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EUS, saprolegniasis, streptococcosis are the most prevalent disease in Narsingdi district.

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Around 140 aqua drugs and chemicals are currently in use for treatment of those diseases.

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About 40 different antibiotics are found in use by the farm managers.

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A proper education of using drugs and chemicals is recommended for the farmers.

From gut to mud: dissemination of antimicrobial resistance between animal and agricultural niches

With increasing reports on antimicrobial resistance (AMR) in humans, animals and the environment, we are at risk of returning to a pre-antibiotic era. Therefore, AMR is recognized as one of the major global health threats of this century. Antibiotics are used extensively in farming systems to treat and prevent infections in food animals or to increase their growth. Besides the risk of a transfer of AMR between the human and the animal sector, there is another yet largely overlooked sector in the One Health triad. Human-dominated ecosystems such as agricultural soils are a major sink for antibiotics and AMR originating from livestock farming. This review summarizes current knowledge on the prevalence of AMR at the interface of animal and agricultural production and discusses the potential implications for human health. Soil resistomes are augmented by the application of manure from treated livestock. Subsequent transfer of AMR into plant microbiomes may likely play a critical role in human exposure to antibiotic resistance in the environment. Based on the knowledge that is currently available we advocate that more attention should be paid to the role of environmental resistomes in the AMR crisis.

The Fate of Foodborne Pathogens in Manure Treated Soil

The aim of this review was to provide an update on the complex relationship between manure application, altered pathogen levels and antibiotic resistance. This is necessary to protect health and improve the sustainability of this major farming practice in agricultural systems based on high levels of manure production. It is important to consider soil health in relation to environment and land management practices in the context of the soil microflora and the introduction of pathogens on the health of the soil microbiome. Viable pathogens in manure spread on agricultural land may be distributed by leaching, surface run-off, water source contamination and contaminated crop removal. Thus it is important to understand how multiple pathogens can persist in manures and on soil at farm-scale and how crops produced under these conditions could be a potential transfer route for zoonotic pathogens. The management of pathogen load within livestock manure is a potential mechanism for the reduction and prevention of outbreaks infection with Escherichia coli, Listeria Salmonella, and Campylobacter. The ability of Campylobacter, E. coli, Listeria and Salmonella to combat environmental stress coupled with their survival on food crops and vegetables post-harvest emphasizes the need for further study of these pathogens along with the emerging pathogen Providencia given its link to disease in the immunocompromised and its’ high levels of antibiotic resistance. The management of pathogen load within livestock manure has been widely recognized as a potential mechanism for the reduction and prevention of outbreaks infection but any studies undertaken should be considered as region specific due to the variable nature of the factors influencing pathogen content and survival in manures and soil. Mediocre soils that require nutrients could be one template for research on manure inputs and their influence on soil health and on pathogen survival on grassland and in food crops.

Spatial and temporal dynamics of microbiomes and resistomes in broiler litter stockpiles

Farmers apply broiler chicken litter to soils to enrich organic matter and provide crops with nutrients, following varying periods of stockpiling. However, litter frequently harbors fecal-derived microbial pathogens and associated antibiotic resistance genes (ARGs), and may be a source of microbial contamination of produce. We coupled a cutting-edge Loop Genomics long-read 16S rRNA amplicon-sequencing platform with high-throughput qPCR that targeted a suite of ARGs, to assess temporal (five time points over a 60-day period) and spatial (top, middle and bottom layers) microbiome and resistome dynamics in a broiler litter stockpile. We focused on potentially pathogenic species from the Enterobacteriaceae, Enterococcaceae and Staphylococcaceae families associated with food-borne disease. Bacterial diversity was significantly lower in the middle of the stockpile, where targeted pathogens were lowest and Bacillaceae were abundant. E. coli was the most abundant Enterobacteriaceae species, and high levels of the opportunistic pathogen Enterococcus faecium were detected. Correlation analyses revealed that the latter was significantly associated with aminoglycoside (aac(6′)-Ib(aka aacA4), aadA5), tetracycline (tetG), vancomycin (vanC), phenicol (floR) and MLSB (mphB) resistance genes. Staphylococcaceae were primarily non-pathogenic, but extremely low levels of the opportunistic pathogen S. aureus were detected, as was the opportunistic pathogen S. saprophyticus, which was linked to vancomycin (vanSA, vanC1), MLSB (vatE, ermB) and tetracycline (tetK) resistance genes. Collectively, we found that stockpile microbiomes and resistomes are strongly dictated by temporal fluctuations and spatial heterogeneity. Insights from this study can be exploited to improve stockpile management practice to support sustainable antimicrobial resistance mitigation policies in the future.

Determination of Colistin in Contents Derived from Gastrointestinal Tract of Feeding Treated Piglet and Broiler

Colistin is considered as the last-resort treatment for multiantibiotic-resistant Gram-negative bacterial infections in humans. However, the oral administration of colistin to livestock and poultry results in the introduction of large amounts of colistin to the surrounding environment via urine and feces, potentially inducing the prevalence of colistin-resistant bacteria and the impact on the ecological environment. We established a quantitative mass spectrometry (MS) based method to measure colistin in contents recovered from the gastrointestinal segments of piglets and broilers, as well as colistin in feces from the animals. The mean recoveries of colistin from different matrices were between 73.2% and 103.9%. The quantitation limit values for different matrices ranged from 0.37 to 1.85 ng/g. In colistin-treated swine samples, the highest concentration of colistin was detected in feces samples at a level of 1248.3 ng/g. However, the highest concentration of colistin in broiler samples was around 4882.9 ng/g, which was found in the contents derived from broilers' ceca. The employment of the proposed method to assess colistin in animals' gastrointestinal tracts might help to understand the colistin absorption in animals' guts and the potential impact of colistin on the emergence of resistant bacteria in animals' gut flora and the ecological environment.

Poultry Litter Contamination by Escherichia coli Resistant to Critically Important Antimicrobials for Human and Animal Use and Risk for Public Health in Cameroon

Residues of antimicrobials used in farm can exert selective pressure and accelerate the occurrence of multidrug resistant bacteria in litter. This study aimed to investigate the resistance profile of Escherichia coli isolated from poultry litter. A total of 101 E. coli strains was isolated from 229 litter samples collected and stored for two months in the laboratory at room temperature. Antimicrobial susceptibility testing was performed using the disk diffusion method. An overall resistance prevalence of 58.4% (95% CI: 48.8-68.0) was obtained with 59 E. coli strains resistant to various antimicrobial agents. High levels of resistance were observed with ciprofloxacin (21/59: 36%), imipenem (27/59: 45%), norfloxacin (44/59: 74%), ceftriaxone (44/59: 74%), and levofloxacin (44/59: 75%). These antimicrobials classified under the Watch group by WHO are indicators of the high AMR risk to public health in Cameroon. Multivariable logistic regression analysis revealed that a greater probability of high level of E. coli multidrug resistance was associated with lack of training in poultry farming (OR = 0.13, p = 0.01), less experience in poultry farming (OR = 11.66 p = 0.04), and the high frequency of digestive tract disease (OR = 0.10; p = 0.001). This study revealed that poultry litter constitutes a potential source of dissemination of resistant germs from farm animals to the environment and humans.