Objective  To understand the molecular types and drug resistance characteristics of Salmonella typhimurium Typhimurium isolated from diarrhea cases in Wuxi city.

  Methods  The antimicrobial susceptibility of 26 Salmonella Typhimurium strains isolated from sentinel hospitals in Wuxi city from 2016 to 2017 was determined by broth microdilution methodto 14 antibiotics. Two multidrug-resistant strains (SM699: resistant to 7 types of antibiotic; SM912: resistant to 4 types of antibiotic) were selected for whole-genome sequencing, and the genetic basis of drug resistance and multilocus sequence typing (MLST) were studied by bioinformatics methods. The homology of strain was analyzed by pulse field gel electrophoresis (PFGE).

  Results  26 Salmonella Typhimurium strains were sensitive to imipenem and showed different degrees of resistance (3.8%−65.4%) to 13 other antibiotics. The drug resistance rates oftetracycline (65.4%, 17/26), ampicillin (61.5%, 16/26) and nalidixicacid (42.3%, 11/26) occupied the top three. Twenty strains (76.9%, 20/26) were resistant to at least one class of antibiotics, with a total of 15 drug-resistant phenotypes, and 14 strains (53.8%, 14/26) were multi-drugresistant strains. The second generation sequencing results showed that SM699 and SM912 carried 23 and 9 resistance genes, respectively, which mediated drug resistance to the corresponding antibiotics. The resistance genes and drug resistance phenotypes were basically consistent. In addition, one point mutationin gyrA of SM699 was found to mediate quinolone resistance. Both strains were ST34 and belonged to the same clone. PFGE showed that 26 strains weredividedinto 23 bands, with the similarity between 58.6%−100.0%.

  Conclusion  The drug resistance of Salmonella Typhimurium in Wuxi wasserious. In order to provide a basis for better prevention strategies, weshould continuously strengthen the monitoring of drug resistance, and further study was needed to clarify the mechanism of drug resistance gene acquisition.