One Health Investigation of Colistin Resistance Transmission Dynamics Between Poultry, Environment, and Humans in Anambra State

Colistin resistance mediated by plasmid-encoded mcr genes represents a critical global health threat, as colistin serves as a last-resort antibiotic for infections with carbapenem-resistant Enterobacteriaceae in human medicine. Colistin has been widely used as a growth promoter and therapeutic agent in Nigerian poultry production. This study conducted a comprehensive One Health investigation of colistin resistance transmission dynamics at the poultry-environment-human interface in Anambra State, South East Nigeria. Bacterial isolates were collected from four compartments: broiler ceca at processing facilities in Awka and Onitsha, poultry farm effluent and surrounding soil, drinking water sources near farms, and rectal swabs from farm workers and community members in neighbouring villages. A total of 480 Enterobacteriaceae isolates were recovered and tested for colistin resistance by broth microdilution. All resistant isolates were subjected to whole-genome sequencing using Illumina short-read technology for mcr gene identification, resistome characterisation, and phylogenomic analysis. Colistin-resistant isolates were recovered from all four compartments with prevalence of 18.7 percent in poultry, 24.3 percent in effluent, 11.2 percent in water, and 8.4 percent in humans. The mcr-1 gene on IncHI2 and IncFIB plasmids was the predominant resistance mechanism. Phylogenomic analysis demonstrated high-confidence genomic relatedness between poultry and human isolates sharing identical sequence types, confirming inter-compartment transmission. Effluent management was identified as the critical transmission node between farm and community. These findings provide genomic evidence for ongoing colistin resistance transmission at a critical One Health interface in Anambra State and inform urgent interventions including colistin use prohibition and effluent treatment mandates. Keywords: colistin resistance, mcr-1, One Health, poultry, Anambra State.