Prevalence and Molecular Characterization of Antimicrobial-Resistant Escherichia coli in Pig Farms, Slaughterhouses, and Terminal Markets in Henan Province of China.

Escherichia coli is an important foodborne pathogen and also plays key roles in dissemination of antimicrobial resistance genes (ARGs). However, current data on the prevalence of antimicrobial-resistant E. coli at different nodes of the pork supplying chain are still limited. Herein, we investigated drug-resistant phenotypes and molecular characteristics of E. coli strains isolated from different pig farms, slaughterhouses, and terminal markets in the Henan Province of China. A total of 191 (70.74%), 140 (35.09%), and 77 (30.20%) E. coli strains were isolated from 270, 399, and 255 samples collected from pig farms, slaughterhouses, and retailing markets, respectively. Antimicrobial susceptibility testing revealed that these 408 strains showed severe antimicrobial resistance profiles. Approximately 93.19% (178/191), 66.43% (93/140), and 67.53% (52/77) of the isolates from farms, slaughterhouses, and terminal markets were resistant to three of the nine antibiotic classes tested, respectively. Multilocus sequence typing showed that sequence types (STs) 10 and ST101 were commonly identified among the isolates from farms, slaughterhouses, and terminal markets. Isolates belonging to these two STs carried multiple ARGs, conferring resistance to the antibiotics tested. Two important ARGs with great public health concerns (mcr-1 and blaNDM-1) were found from these two STs. Isolates belonging to these two STs also carried several virulence factor-encoding genes, including astA, tsh, and traT, which might contribute to the pathogenesis of these isolates. The wide prevalence and distribution of these two STs in different nodes of pork supplying chain might represent a big public health threat and should receive more attention.