Contamination status, drug resistance and molecular epidemiological characteristics of Salmonella strains isolated from stinky tofu sold in markets in Ma'anshan, Anhui

  Objective  To investigate the contamination status, serotype distribution, drug resistance and molecular epidemiological characteristics of Salmonella strains isolated from stinky tofu sold in markets in Ma'anshan, Anhui, and explore the relationship between different serotype, molecular type and drug resistance of Salmonella.

  Methods  Stinky tofu and the auxiliary materials of them were collected from the markets in Ma'anshan from June to September 2020 for Salmonella detection. The drug susceptibility of the strains isolated was tested by micro broth dilution. Pulsed field gel electrophoresis (PFGE) and multi-locus sequence typing (MLST) were used for molecular typing of the strains. The map of PFGE, drug susceptibility and MLST results were analyzed by using BioNumerics 7.6.

  Results  The detection rate of Salmonella strains in stinky tofu was 10.3% (25/242) in Ma'anshan, Salmonella was detected in both auxiliary materials and process environment. The strains isolated could be divided into 6 serotypes and one unspecific serotype. The drug resistance rates to tetracycline, ampicillin and streptomycin were 48.3%, 34.5% and 31.0%, respectively. The strains could be divided into 9 PFGE types and 6 STs. The Simpson diversity index of the isolates were 0.711, 0.762 and 0.753 by serologic test, PFGE and MLST, respectively.

  Conclusion  The contamination rate of Salmonella strains in stinky tofu sold in markets was high in Ma'anshan, Salmonella contamination existed in the process of stinky tofu. There were some homology relationships among isolates from different areas.