Colistin Resistance Gene mcr-1 and Its Variant in Escherichia coli Isolates from Chickens in China

Abstract

The mcr-1 gene was detected in 5.11% (58/1136) of Escherichia coli isolates of chicken origin from 13 provinces in China. A novel mcr-1 variant, named mcr-1.3, encoding an Ile-to-Val functional variant of MCR-1 was identified in a sequence type 155 (ST155) strain. An mcr-1.3-containing IncI2 plasmid, pHeN867 (60,757 bp), was identified. The transfer of pHeN867 led to a 32-fold increase in the MIC of colistin in the recipient, exhibiting an effect on colistin resistance that was similar to that of mcr-1.

Keywords: E. coli; colistin resistance; mcr-1.3; plasmid.

FIG 1

PFGE patterns of chromosomal DNA restriction fragments from 58 mcr-1-positive E. coli strains from chickens. CST, colistin; CTX, cefotaxime; AMC, amoxicillin-clavulanic acid; CAZ, ceftazidime; IPM, imipenem; CIP, ciprofloxacin; LVX, levofloxacin; NAL, nalidixic acid; AMK, amikacin; GEN, gentamicin; DOX, doxycycline; SXT, trimethoprim-sulfamethoxazole; STR, streptomycin; ATM, aztreonam; PIP, piperacillin; ST, sequence type.

FIG 2

Plasmid structures of pHeN867, pHNSHP45, and pAF23. Light blue shading denotes shared regions of homology. ORFs are indicated by arrows and colored based on their predicted gene functions.