Similar Antimicrobial Resistance of Escherichia coli Strains Isolated from Retail Chickens and Poultry Farms.

Antimicrobial resistance (AMR) is a major public health challenge and spreads through humans, animals, and the environment. Many reports show that AMR genes (ARGs) or phenotypes can be transferred from food animals to humans. However, the level and correlation of AMR in different nodes of the poultry meat supply chain are still poorly understood. Herein, 225 Escherichia coli isolates were recovered from chilled chicken samples from markets (123) and chicken fecal samples from farms (102) in Zhejiang Province, China. The dominant sequence types (STs) were ST155 (8.89%), ST48 (7.56%), and ST10 (7.11%), which are common in chicken and fecal samples. Antimicrobial susceptibility testing (AST) analysis showed that the E. coli isolates from fecal samples and retail chickens were resistant to ampicillin (61.77% and 63.42%, respectively) and trimethoprim (56.87% and 52.85%). Moreover, 36.59% of the E. coli isolates from chilled chickens and 39.22% of the isolates from fecal samples were resistant to three or more antimicrobial agents. A total of 59 ARGs were identified in sequenced E. coli genomes, including the mcr-1 gene involved in colistin resistance. The E. coli from farms and markets could be clustered in the same branch according to core single nucleotide polymorphisms. In addition, toxin genes astA and hlyE were also predicted in 86.5% (32/37) and 13.5% (5/37) of the above genomes, respectively. Taken together, these findings demonstrated that E. coli isolates from markets and farms showed similar AMR patterns, suggesting that E. coli strains in markets may originate from farms.