Abstract:
The rise of the plasmid-encoded colistin resistance gene
mcr-1 is a major concern globally. Here, during a routine surveillance, an unexpectedly high prevalence of
Escherichia coli with reduced susceptibility to colistin (69.9%) was observed in a Chinese broiler farm. Fifty-three (63.9%)
E. coli isolates were positive for
mcr-1. All identified
mcr-1-positive
E. coli (MCREC) were multidrug resistant and carried other clinically significant resistance genes. Furthermore, the
mcr-1 genes were mainly located on the IncI2 and IncHI2 plasmids. Conjugation experiments unraveled the co-transfer of
mcr-1 with other antibiotic resistance genes (
blaCTX-M-55,
blaCTX-M-14,
floR, and
fosA3) via the IncI2 (
n=3) and IncHI2 (
n=4) plasmids. The stable genetic context
mcr-1-
pap2 was common in the IncI2 plasmids, whereas IS
Apl1-
mcr-1-
pap2-IS
Apl1 was mainly found in the IncHI2 plasmids. The dominance of
mcr-1-bearing IncI2 and IncHI2 plasmids and co-selection of
mcr-1 with other antimicrobial resistance genes might contribute to the exceptionally high prevalence of
mcr-1 in this broiler farm. Our results emphasized the importance of appropriate antibiotic use in animal production.