Phenotypic and Genotypic Characterisation of Antimicrobial-Resistant Organisms in Family Medicine Outpatient Settings in Nigeria: Implications for Stewardship Policy

Background: The family medicine outpatient setting is a critical, yet understudied, reservoir and transmission point for antimicrobial-resistant organisms in Nigeria. Comprehensive characterisation of resistance patterns and their molecular determinants is necessary to inform context-specific stewardship policy. Methodology: A multi-centre cross-sectional microbiological study collected clinical specimens from 600 family medicine outpatients with suspected bacterial infections across sites in Lagos, Kano, Enugu, Port Harcourt, Maiduguri, and Abuja. Standard microbiological culture, antibiotic susceptibility testing, and whole-genome sequencing of selected isolates were performed. Stewardship implications were synthesised using a policy analysis framework. Results: Extended-spectrum beta-lactamase-producing Enterobacteriaceae were detected in a substantial proportion of isolates. Multi-drug resistant Staphylococcus aureus was prevalent in dermatological specimens. Resistance to fluoroquinolones and third-generation cephalosporins was high. Whole-genome sequencing revealed international high-risk resistance clones circulating across multiple geopolitical zones. Conclusion: The family medicine outpatient setting in Nigeria harbours diverse antimicrobial-resistant organisms with genotypic characteristics indicative of both community transmission and hospital spillover. These findings provide original evidence supporting the urgency of primary care-specific antibiotic stewardship programmes and diagnostic capacity strengthening. Keywords: antimicrobial resistance, family medicine, whole genome sequencing, stewardship, Nigeria