Prevalence of colistin resistance and mcr-1/mcr-2 genes in ESBL/AmpC-producing E. coli isolated from chickens in Canada (Quebec), Senegal and Vietnam.

OBJECTIVES: This study investigated the prevalence of E. coli colistin resistance and mcr-1 and mcr-2 genes among ESBL/AmpC-producer E. coli isolates recovered from chicken feces in Canada (Quebec), Senegal and Vietnam, and evaluated the susceptibility pattern of the colistin-resistant E. coli isolates to other clinically relevant antimicrobials.

METHODS: A total of 327 potential ESBL/AmpC-producing E. coli isolates from chicken farms in Canada (Quebec), Senegal and Vietnam, were analysed for colistin susceptibility by broth microdilution method and for the presence of the mcr (1-2) genes by PCR. The pmrA and pmrB genes of colistin resistant E. coli isolates, in absence of mcr (1-2) genes were sequenced. Antimicrobial resistance phenotypes of colistin-resistant E. coli isolates were determined by disk diffusion.

RESULTS: None of the 108 potential ESBL/AmpC-producing E. coli isolates from 7 farms in Canada were colistin-resistant or possessed mcr-1 or mcr-2. A low prevalence of 2.2 % of colistin resistance was observed in 93 Senegalese isolates from the 15 sampled farms although neither mcr-1 nor mcr-2 was found. A prevalence of 8.7% of colistin resistance was observed among 126 Vietnamese isolates from 2 of the 4 sampled farms. The mcr-1 gene was detected in 85% of the 13 phenotypically colistin resistant isolates. Moreover, all colistin resistant isolates presented a multidrug resistant phenotype.

CONCLUSIONS: The co-existence of the mcr-1 and ESBL/AmpC genes and the very high level of multiple drug resistance in all colistin resistant E. coli isolates obtained from sampled chicken farms in Vietnam is a major concern.