Subtyping of Salmonella isolates on retail raw chicken in China by pulsed-field gel electrophoresis and plasmid analysis

Salmonellosis is one of the most common bacterial foodborne diseases worldwide. Poultry and poultry products are considered significant vehicles for foodborne salmonellosis transmission. We subtyped 725 Salmonella isolates recovered from 1152 retail raw chickens using pulsed-field gel electrophoresis (PFGE), and 448 ampicillin-resistant ones among 725 isolates using plasmid analysis in this study. Based on 80% similarity, 126 PFGE clusters were identified among 725 Salmonella isolates. Sixty one (8.4%) of 725 isolates belonged to PFGE cluster C96, followed by cluster C5 (38/725, 5.2%), and cluster C18 (38/725, 5.2%). Fifty two distinct PFGE patterns were detected among the isolates in Shaanxi Province, and 67, 64, 82, 67, 55, 88, and 47 patterns were identified in isolates in Henan, Sichuan, Beijing, Guangxi, Shanghai, Guangdong, and Fujian, respectively. Plasmids were detected in 331 (73.9%) of the 448 ampicillin-resistant Salmonella isolates. One hundred and twenty three plasmid profiles were identified, and P3, P11, P30, P12, were defined as predominant ones. Combination of PFGE and plasmid analysis was an effective way to enhance the genotypic discrimination ability to Salmonella, especially for S. Typhimurium isolates. Our results indicated that multiple Salmonella subtypes were prevalent in retail raw chicken in China, and they were potential hazard for food safety.