Clonal Spread of Escherichia coli ST93 Carrying mcr-1 -Harboring IncN1-IncHI2/ST3 Plasmid Among Companion Animals, China.

The purpose of this study was to investigate the occurrence of plasmid-mediated colistin resistance gene mcr-1 in Enterobacteriaceae isolates from companion animals in Guangzhou, China. Enterobacteriaceae isolated from 180 samples collected from cats and dogs were screened for mcr-1 by PCR and sequencing. MCR-1-producing isolates were further characterized by multilocus sequence typing and pulsed-field gel electrophoresis (PFGE). Plasmid characterization was performed by conjugation, replicon typing, S1-PFGE, and Southern blot hybridization. Plasmid pHN6DS2 as a representative IncN1-IncH12/ST3 plasmid from ST93 E. coli was fully sequenced. pHN6DS2-like plasmids were screened by PCR-mapping and sequencing. The mcr-1 gene was detected in 6.25% (8/128) Escherichia coli isolates, of which, five belonged to E. coli ST93 and had identical PFGE patterns, resistance profiles and resistance genes. mcr-1 genes were located on similar to 244.4 kb plasmids (n = 6), similar to 70 kb plasmids, and similar to 60 kb plasmids, respectively. Among them, five mcr-1-carrying plasmids were successfully transferred to recipient by conjugation experiments, and were classified as IncN1-IncH12/ST3 (similar to 244.4 kb, n = 4, all obtained from E. coli ST93), and Inc12 (similar to 70 kb, n = 1), respectively. Plasmid pHN6DS2 contained a typical IncHI2-type backbone, with IncN1 segment (Delta repA-Iteronsl-gshB-Delta IS1294) inserted into the multiresistance region, and was similar to other mcr-1-carrying IncH12/ST3 plasmids from Enterobacteriaceae isolates of various origins in China. The remaining five mcr-1-bearing plasmids with sizes of similar to 244.4 kb were identified to be pHN6DS2-like plasmids. In conclusion, clonal spread of ST93 E. coli isolates was occurred in companion animals in Guangzhou, China.