Study on molecular epidemiology and antibiotic resistance of Salmonella Wandsworth

Objective To understand the molecular epidemiological and antibiotic resistant characteristics of Salmonella Wandsworth in Shanghai. Methods Antibiotic susceptibility test and pulsed field gel electrophoresis (PFGE) were conducted for S. Wandsworth strains isolated form diarrhea cases, environment samples and food samples in Shanghai. Results A total of 4 553 clinical Salmonella strains were isolated by the laboratory network in Shanghai from 2005 to 2012. The top 10 serotypes included 20 serotypes and all belonged to A-F serogroups, while S. Wandsworth was the most common serotype in rare non-A-F serogroups. People aged60 years and children aged5 years are susceptible to S. Wandsworth. Bloodstream infection is rarely observed. Totally 1805 Salmonella strains were isolated from food and environment samples, and the strains in top 10 serotypes had more multiformity than the strains from human. S. Wandsworth strains, most common among rare serotypes, were mainly isolated form bullfrogs, green turtles, freshwater fish and sea fish. There was no significant difference in antibiotic resistance between human source strains and other source strains (P0.05). The S. Wandsworth strains isolated belonged to 5 clones indicated by PFGE, the strains in clone A were multi-drug resistant. Moreover, 2 ACSSuT-SH009 cluster strains which were resistant to 12 antimicrobials and SH009 strain from green turtle resistant to 6 antibiotics shared 100% homology. The strains in clone B, D and E were from adults, and the strains in clone C were from young children, all of these strains were sensitive to antibiotics. Conclusion Although S. Wandsworth is rare serotype, the infection caused by this pathogen increased in recent years. Highly homologous was found among the S. Wandsworth strains isolated from bullfrog, green turtle, freshwater fish and sea fish in Shanghai. It is necessary to strengthen the surveillance for pathogenic MDR clones and the early warnings of the risk of cross contamination and contact infections in preparing bullfrog and green turtle foods.