Distribution and Molecular Characterization of Escherichia coli Harboring mcr Genes Isolated from Slaughtered Pigs in Thailand.

The resistance of Enterobacteriaceae to colistin mediated by plasmid-borne mobile mcr genes is an emerging public health concern. This study aimed to explore the distribution and characteristics of Escherichia coli isolates harboring mcr genes from slaughtered pigs in Thailand from 2014 to 2015. A total of 779 E. coli isolates were assessed, of which 61 (7.8%) were found to carry mcr genes, including mcr-1, mcr-3, mcr-6, mcr-7, mcr-8, and mcr-9, together with co-occurrences of mcr-1+mcr-3, mcr-1+mcr-9, and mcr-3+mcr-6+mcr-7. In these mcr-harboring E. coli isolates, mcr-1 (40.9%) and mcr-9 (32.8%) were predominant. Colistin resistance was mainly mediated by the mcr-1 gene, whereas intermediate resistance was noted in isolates that harbored mcr-9, mcr-6, mcr-7, and mcr-8 genes. Most E. coli isolates harboring mcr genes were susceptible to third-generation cephalosporins and all of these isolates were susceptible to carbapenems. Clermont phylotyping demonstrated that mcr-harboring isolates mainly belonged to phylogroup A (44.3%), followed by phylogroups B1 (34.4%), D (14.8%), and B2 (6.6%). Multilocus sequence typing revealed that 25 sequence types (STs) were assigned to 45 mcr-harboring E. coli isolates, whereas the remaining 16 isolates were novel STs. The mcr-1 and mcr-9 genes were mostly predominant in ST101 and ST8900, respectively. This study provides a comprehensive insight into the prevalence and diversity of mcr-harboring E. coli isolates obtained from slaughtered pigs across Thailand. Strengthening of surveillance systems by the government for controlling and preventing mcr dissemination from animals to humans or vice versa is urgently needed. No clinical trial registration number.