Prevalence of Colistin Resistance Genes in Enterobacteriaceae Isolated from Humans and Livestock in Borno State: A One Health Approach

The emergence of plasmid-mediated colistin resistance mediated by mcr genes in both human clinical and animal-associated bacteria represents a critical threat to last-resort antibiotic therapy for carbapenem-resistant Gram-negative infections. This One Health cross-sectional study investigated the prevalence of mcr-1 and mcr-2 colistin resistance genes in Enterobacteriaceae from humans and livestock across Maiduguri metropolis and surrounding pastoral communities, Borno State, in the North East geopolitical zone of Nigeria. Rectal swabs from 120 healthy volunteers and 150 cattle, goats, and poultry were collected. Enterobacteriaceae were isolated and confirmed by conventional biochemical methods. Colistin susceptibility was assessed by broth microdilution, and mcr gene detection was performed by multiplex PCR followed by Sanger sequencing. mcr-1 was detected in 9.2 percent of human isolates and 16.7 percent of animal isolates. mcr-2 was detected in 3.3 percent of human and 5.3 percent of animal isolates. Identical mcr-1 sequence variants were found in human and animal isolates from the same households, suggesting cross-species transmission. Colistin use as a veterinary growth promoter was documented by 43 percent of surveyed livestock farmers. These findings provide the first documented evidence of mcr-mediated colistin resistance in Borno State and highlight interspecies transmission dynamics warranting urgent One Health surveillance and colistin regulation in veterinary practice. Keywords: colistin resistance, mcr genes, One Health, Borno State, Enterobacteriaceae.