Serotype distribution and antimicrobial resistance characteristics of Salmonella in chicken meat collected from wholesale markets in Beijing City

ObjectiveTo investigate the serotype distribution and antimicrobial resistance characteristics of Salmonella isolated from retail chicken in Beijing City.MethodsA total of 135 Salmonella strains were isolated from retail chicken meat collected from three large wholesale markets in Fengtai District in Beijing City from 2014 to 2015. The serotype of these Salmonella strains was identified using both a Luminex serotyping kit and a traditional serum agglutination method. Multilocus sequence typing was performed according to the recommended conditions of the Enterobase database. Antimicrobial susceptibility testing plates were used to determine the susceptibility of the isolates against 12 classes of drugs representing 25 antimicrobial agents. PCR was used to detect the prevalence of the 10 mobile colistin resistance genes （mcr） and three NDM-type carbapenemases genes （blaNDM）.ResultsAmong the 135 Salmonella strains， 6 serogroups were detected， with D1 and B being the main serogroups； 20 serotypes were detected， in which Enteritidis， Indiana， and Thompson were the dominant ones with percentages of 50.4%， 15.6%， and 8.1%， respectively； 21 ST types were obtained， and a good correspondence was observed between serotypes and ST types. 91.9% of all tested isolates showed resistance to the tested drugs and showed the highest resistance to nalidixic acid， ampicillin， ampicillin-sulbactam， tetracycline. Multi-drug resistant strains accounted for 71.1% of all strains and were resistant to as many as 18 kinds of antimicrobial compounds belonging to 10 categories. Among the 17 strains co-resistant to 8 or more classes of drugs， 16 were of the Indiana serotype. The proportion of strains with high multi-drug resistance was different in different packaging methods， different seasons， and different wholesale markets. All strains were negative for the mcr and blaNDM genes.ConclusionThe serotypes of Salmonella isolates from chicken meat in wholesale markets in Beijing City from 2014 to 2015 were complex， with the dominant serotype of Salmonella Enterititis， and the overall antimicrobial resistance level of all isolates was high. To assess the possible food safety risks， continuous monitoring for Salmonella Indiana with high levels of antimicrobial resistance must be carried out and their drug resistance and transmission mechanisms must be studied to help develop first-line and ultimate drugs for clinical treatment of Salmonella diseases.