Surveillance study of the prevalence and antimicrobial resistance of Salmonella in pork from open markets in Xuzhou, China

Salmonella is considered one of the most important foodborne pathogens and is commonly associated with the consumption of pork and other animal products. Multidrug resistant (MDR) Salmonella strains are highly adaptive and have been responsible for foodborne disease outbreaks. We investigated Salmonella prevalence and antimicrobial resistance in pork obtained from open markets in Xuzhou, Jiangsu Province, China. From October 2016 to September 2017, a total of 155 Salmonella isolates were recovered from 324 pork samples in different open markets, representing 35.5% of the samples tested. All of the Salmonella isolates were characterized using serotyping, antimicrobial resistance detection, and multilocus sequence typing (MIST). Thirteen serotypes were identified among the 155 Salmonella enterica isolates. S. Derby (28.7%) was the most prevalent serotype, but others, such as S. Enteritidis (18.3%), S. Meleagridis (15.7%), and S. Typhimurium (13.0%), were also widespread. MLST analysis showed that 14 sequence type (ST) patterns were identified and ST40 occupied an absolute superiority among these isolates. Tests of susceptibility to 16 antimicrobial agents using a disk diffusion assay showed that 97.4% of the isolates were resistant to at least one compound, and 66.1% exhibited multidrug resistance, as they were resistant to at least four antimicrobials. The presence of most of the antimicrobial resistance genes was consistent with the resistance phenotypes. Of the antimicrobial resistance genes examined in this study, parC, gyrA, aadA1, sul1, floR, and tetA were the most prevalent resistance genes in the MDR isolates. Our findings show the prevalence of Salmonella in pork in the open markets of Xuzhou, China. Additionally, many Salmonella isolates were resistant to multiple antimicrobial agents, which may aid the optimization of hazard analysis in pork sold in open markets.