Comparative phenotypes of Salmonella Typhimurium reveal ST associated biofilm and antibiotic-resistant traits

Salmonella Typhimurium is one of the leading foodborne pathogens. This bacterium can form biofilms on biotic and abiotic surfaces, contributing to the antimicrobial failure. Hence, the emergence of antibiotic-resistant Salmonella with strong biofilm-forming capabilities increases the challenge of sterilization processes, posing a major threat to public health and food safety. In this study, we screened 27 foodborne S. Typhimurium strains isolated during 2013-2017 in Hangzhou. The multilocus sequence typing revealed that 11 (40.74%) was ST19, 10 (37.04%) was ST34, 5 (18.52%) was ST36, and 1 (3.70%) was ST99. The antimicrobial susceptibility test indicated that 11 (40.74%) strains exhibited a multidrug-resistant phenotype, 11 (40.74%) strains were specific antibiotic resistance, and 5 strains (18.52%) were antibiotic sensitive whereas 4 (80%) of ST36 ones showed resistance. Moreover, S. Typhimurium ST36 isolates exhibited a moderate to strong biofilm production capacity, followed by ST34 and ST19. The SEM results clearly demonstrated that ST36 exhibited a higher capacity for (extracellular polymeric substance) EPS release, indicating its superior biofilm-forming ability. In contrast, ST19 displayed an agglomeration phenomenon without concurrent EPS production, signifying its weaker biofilm-forming capability. Overall, emphasizing the spread of S . Typhimurium ST36 and ST34 in Hangzhou, with strong biofilm-forming ability and antibiotic resistance. Therefore, the occurrence of Salmonella Typhimurium ST36 and ST34 in food sources was monitored and appropriate measures should be taken to control Salmonella infection by reducing the formation of biofilms.