Emergence of mcr-1 Gene in Colistin-Resistant Escherichia coli Isolates from Chicken in Chitwan, Nepal

The escalating prevalence of colistin-resistant Escherichia coli in poultry has emerged as a significant concern. This study aimed to assess the occurrence of the mcr-1 gene in colistin-resistant E. coli isolates from poultry samples. A cross-sectional study was conducted at National Avian Disease Investigation Laboratory, Nepal, on 210 chicken meat samples, including liver, heart, and spleen. E. coli was isolated and identified by conventional cultural methods. Antibiotic resistance pattern was assessed by the Kirby-Bauer disc diffusion method. The mcr-1 gene was detected by conventional polymerase chain reaction. The average viable count in chicken meat samples was log 6.01 CFU (colony-forming unit)/g, whereas the average coliform count was log 3.85 CFU/g. Coliforms were detected in at least one sample from 48.01% of total samples. The prevalence of E. coli in all meat samples was 39.52%. Liver accounted for the largest fraction of E. coli isolates (45.45%). Cefepime was the most effective antibiotic. Among all isolates, 45 (54.21%) were multidrug-resistant E. coli, 17 (20.48%) were colistin-resistant E. coli, and 11 (64.70%) harbored the mcr-1 gene. High prevalence of multidrug-resistant E. coli isolates, colistin-resistant isolates, and mcr-1 gene-carrying isolates indicates a serious concern, as it could potentially lead to colistin resistance in human pathogens through horizontal transfer of resistant genes from poultry to humans.