Antibiotic resistance in chicken gut bacteria: a study on bacterial diversity and drug sensitivity in some Nigerian poultry farms

The rising prevalence of multidrug-resistant (MDR) bacteria in poultry, particularly in chickens, poses a serious public health risk, as these pathogens can be transmitted to humans, causing difficult-to-treat gastroenteritis. Therefore, this study was designed to isolate and characterize multidrug-resistant bacteria in poultry chickens, as well as to determine the antibiotic susceptibility and plasmid profiles of resistant bacterial isolates. A total of 360 samples were collected from the cloacae, mouth, and nares of poultry-chickens and analyzed bacteriologically, with antibiotic susceptibility testing conducted following standard microbiological procedures. Plasmid analysis and curing were performed to assess molecular weight and identify resistance mechanisms, whether plasmid-mediated or not. The MDR bacteria isolated from poultry-chickens included Proteus mirabilis (65, 43.6%), Escherichia coli (50, 33.6%), Pseudomonas aeruginosa (7, 4.7%), Serratia marcescens (6, 4.0%), Serratia fonticola (5, 3.4%), Klebsiella oxytoca (3, 2.0%), Klebsiella pneumoniae (2, 1.3%), Salmonella enterica subsp. diarizonae (1, 0.7%), Shigella sonnei (1, 0.7%), Shigella flexneri (1, 0.7%), Escherichia vulneris (1, 0.7%), Enterobacter aerogenes (1, 0.7%), and Morganella morganii (1, 0.7%). Out of the 360 poultry samples analyzed, 137 (38.1%) bacterial isolates were resistant to at least three classes of antibiotics, indicating a high level of multidrug resistance among the isolates. All gastroenteric bacterial isolates (n = 137) showed 100% resistant to both meropenem and cephalosporin, but showed minimal resistance to amikacin (2.9%), making it the most effective antibiotic against these bacteria. Plasmid profiling on ten MDR isolates revealed the presence of at least one plasmid band ranging from 500 bp to 10 kbp, suggesting a possible role of plasmids in mediating antibiotic resistance. These findings underscore the serious implications of antibiotic resistance in poultry and highlights the link between plasmids and resistance, emphasizing the importance of carefully monitoring antibiotic use in developing countries, particularly in poultry farms.