Abstract: A total of 32 Salmonella Typhimurium monophasic variant (S. 1,4,[5],12:i:-) isolates from foods and humans were analyzed for virulence factors and mobile genetic elements by whole genome sequencing, and a phylogenetic tree was then constructed. The acid resistance, biofilm formation capacity, cell adhesion and invasion of these isolates were measured to clarify their virulence characteristics. The results showed that both the food- and human-borne strains harbored a large number of virulence factors and mobile genetic elements such as genomic islands, transposon. Evolutionary relationship analysis showed that all tested strains were closely related to the reference S. 1,4,[5],12:i:- in the database. Moreover, all strains remained viable for 1 hour at pH 3, and 25% of the strains exhibited a high capacity for biofilm formation. However, no significant differences in biofilm formation, cell adhesion or invasion ability were observed between the human- and food-borne isolates. In conclusion, the S. 1,4,[5],12:i:- isolates from different sources harbored a large number of virulence factors and mobile genetic elements, and their virulence-related phenotypes were heterogeneous. These findings provide important data support for the risk assessment of S. 1,4,[5],12:i:-.

Key words: Salmonella Typhimurium monophasic variant; virulence factors; acid resistance; biofilm; cell adhesion and invasion