Antimicrobial resistance profiles and characteristics of integrons in Escherichia coli strains isolated from a large-scale centralized swine slaughterhouse and its downstream markets in Zhejiang, China

The pork production chain and raw pork products are among the most important reservoirs of antimicrobial-resistant microorganisms. This study investigated the antimicrobial resistance profiles and integrons and their associated gene cassettes of Escherichia coli isolated from a large-scale centralized swine slaughterhouse in Zhejiang, China and its downstream markets. A total of 300 E. coli isolates were identified from 720 samples. No E. coli isolates were detected on the slaughtering line or at downstream supermarkets. Of the 300 E. coli isolates collected from lairages and downstream open markets, 242 (80.67%) were classified as multi-drug resistant (MDR). In addition, the prevalence of multi-drug resistance was significantly different (p < 0.05) and antimicrobial resistance profiles varied among the different sampling points. Furthermore, of 300 E. coli strains, 76 (25.33%) were positive for class 1 integrons and nine (3.00%) were positive for class 2 integrons. Three different gene cassettes were detected in class 1 integrons and one gene cassette was detected in class 2 integrons. Our study demonstrates that E. coli isolates from lairages and open markets are frequently MDR, and suggests that precautionary measures and hygienic environments are necessary to prevent the spread of antimicrobial-resistant microorganisms and their mobile genetic elements through the food chain.