Molecular Mechanisms of Antimicrobial Resistance in Campylobacter Isolated from Poultry and Human Clinical Cases in South West Nigeria

Campylobacter species are the most common bacterial cause of foodborne gastroenteritis globally, and resistance to fluoroquinolones and macrolides threatens therapeutic options. This study investigated the molecular mechanisms of antimicrobial resistance in Campylobacter isolated from poultry and human clinical cases in South West Nigeria, spanning Ogun, Oyo, Ondo, Ekiti, Osun, and Lagos States. A comparative genomic study was conducted using whole-genome sequencing of 200 Campylobacter isolates collected from broiler carcasses at retail and 80 clinical human isolates from outpatient gastroenteritis cases. Resistance genes, mutations in gyrA and 23S rRNA, and mobile genetic elements were identified and compared between animal and human isolates. Fluoroquinolone resistance was detected in 72.5% of poultry isolates and 61.3% of clinical isolates, predominantly mediated by the gyrA C-257-T mutation. Erythromycin resistance rates were 38% in poultry and 29.3% in clinical isolates, associated with 23S rRNA A2075G mutations. Genomic comparison revealed 18 shared multilocus sequence typing sequence types between human and poultry populations, with several dominant clones carrying identical resistance profiles, suggesting direct zoonotic transmission. The study provides a comprehensive molecular resistance landscape for Campylobacter at the poultry-human interface in South West Nigeria and contributes original genomic evidence of zoonotic clone sharing. Fluoroquinolone stewardship in poultry production and enhanced clinical surveillance are urgently recommended. Keywords: Campylobacter, antimicrobial resistance, whole genome sequencing, poultry, South West Nigeria