Molecular Characterisation of Antimicrobial Resistance Genes in Escherichia coli Isolates from Poultry in South West Nigeria

The widespread prophylactic and therapeutic use of antibiotics in Nigerian poultry production has selected for multidrug-resistant Escherichia coli strains that can serve as reservoirs of resistance genes transferable to human pathogenic bacteria through horizontal gene transfer. Characterising the molecular basis of resistance in poultry E. coli is essential for understanding resistance transmission dynamics and informing antibiotic stewardship strategies. This study isolated E. coli from cloacal swabs of broiler chickens at farms in Ogun and Lagos states, South West Nigeria, and characterised antimicrobial resistance by phenotypic susceptibility testing and molecular detection of resistance determinants. One hundred and fifty E. coli isolates were recovered from 300 cloacal swabs. Disk diffusion susceptibility testing revealed resistance rates of 92.7 percent to tetracycline, 88 percent to ampicillin, 74 percent to trimethoprim-sulphamethoxazole, 61.3 percent to enrofloxacin, and 47.3 percent to cefotaxime. Multidrug resistance was observed in 82.7 percent of isolates. PCR-based detection identified blaTEM in 71.3 percent of isolates, tetA in 64 percent, aadA in 58.7 percent, and sul2 in 55.3 percent. The mcr-1 colistin resistance gene was detected in 8 percent of isolates, representing the first report from South West Nigeria. Extended-spectrum beta-lactamase production was confirmed in 38 percent of isolates by the double disk synergy test. These findings demonstrate the alarming prevalence of mobile resistance determinants in poultry E. coli from South West Nigeria and underscore the need for targeted surveillance, antibiotic use regulation, and public health risk assessment in the poultry-human interface. Keywords: antimicrobial resistance, Escherichia coli, poultry, blaTEM, South West Nigeria.