Frequency of mcr-1 gene in commensal Escherichia coli in broiler chicken in Bangladesh

Colistin is a last-resort antimicrobial for the treatment of critical bacterial infections, and increased occurrence of colistin-resistant bacteria in livestock is of alarming concerns. Colistin and other critical antimicrobials are still widely used in the poultry industry in Bangladesh. Prevalence, distribution and genetic reasons for colistin resistance in the E. coli population in broiler chicken is, however, still unknown. We aimed to investigate the dynamics and genetic diversity of colistin-resistant, commensal E. coli from broiler chicken throughout the production period. A total of 1200 E. coli strains were randomly isolated from 60 pooled fecal samples from 20 broiler farms at three-time points in the production (day-1, day-15, and day-28). Strains were screened for mcr-1 to mcr-5 genes by amultiplex PCR, and their genetic diversity was measured by repetitive extragenic palindromic (REP)-PCR fingerprinting. The dominant REP-types among the mcr-positive isolates were selected for WGS.