Serovar diversity and antimicrobial resistance of non-typhoidal Salmonella enterica recovered from retail chicken carcasses for sale in different regions of China

Non-typhoidal Salmonella enterica (NTS), the etiological agents in foodborne salmonellosis, is a major public health concern. This study describes the serovar diversity and antimicrobial resistance phenotypes identified in NTS isolates from retail whole chicken carcasses across six provinces of China. From food samples tested, a total of 2210 Salmonella isolates were recovered and these were serotyped by conventional and molecular serotyping methods and tested for their susceptibility to a panel of antimicrobial compounds. Sixteen serogroups and 52 serovars were identified, with serogroups B, D1 and C1 common among Enteritidis, Indiana and Infantis isolates. The serovar distribution varied both geographically and seasonally. Most (80.18%) of these isolates were found to be resistant to at least one antimicrobial compound and 54.6% were multi-drug resistant (MDR). Resistance to nalidixic acid (NAL) was common (70.6%) among the 11 tested compounds and no isolate was found to be resistant to carbapenems. There were 119 antimicrobial resistance profiles identified in the study collection. Two-hundred eighty-four isolates, including 99 Salmonella enterica serovar Indiana (S. Indiana), were resistant to seven or eight classes of antimicrobial compound. One-hundred eighty-three S. Indiana isolates were found to be co-resistant to ciprofloxacin and cefotaxime and 179 of these were confirmed as extended-spectrum β-lactamase producers. These data begin to describe the serovar diversity and antimicrobial resistance of NTS isolates recovered from retail chicken carcasses in parts of China. The findings highlight the emergence of ciprofloxacin and cefotaxime co-resistant S. Indiana, a feature displaying serious antimicrobial resistance but not commonly reported in human infections of Salmonella until recently. The food safety implications of these findings are discussed.