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 in Enterobacteriaceae isolates from companion animals in Guangzhou, China. Enterobacteriaceae isolated from 180 samples collected from cats and dogs were screened for 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-IncHI2/ST3 plasmid from ST93 was fully sequenced. pHN6DS2-like plasmids were screened by PCR-mapping and sequencing. The gene was detected in 6.25% (8/128) isolates, of which, five belonged to ST93 and had identical PFGE patterns, resistance profiles and resistance genes. genes were located on ∼244.4 kb plasmids ( = 6), ∼70 kb plasmids, and ∼60 kb plasmids, respectively. Among them, five -carrying plasmids were successfully transferred to recipient by conjugation experiments, and were classified as IncN1-IncHI2/ST3 (∼244.4 kb, = 4, all obtained from ST93), and IncI2 (∼70 kb, = 1), respectively. Plasmid pHN6DS2 contained a typical IncHI2-type backbone, with IncN1 segment (Δ Iterons I- -ΔIS ) inserted into the multiresistance region, and was similar to other -carrying IncHI2/ST3 plasmids from Enterobacteriaceae isolates of various origins in China. The remaining five -bearing plasmids with sizes of ∼244.4 kb were identified to be pHN6DS2-like plasmids. In conclusion, clonal spread of ST93 isolates was occurred in companion animals in Guangzhou, China.