Antimicrobial Resistance and Genomic Characterization of Salmonella Serovars Typhimurium and 4,[5],12:i:- in Huzhou, China.

Salmonella serovar Typhimurium (S. Typhimurium) and its monophasic variant, Salmonella 4,[5],12:i:-, have become two of the most frequently isolated serovars worldwide, in both humans and animals. This study investigated the antimicrobial resistance and genomic characteristics of these two serovar Salmonella. Between 2021 and 2023, a total of 90 S. Typhimurium and Salmonella 4,[5],12:i:-were collected from clinical and food samples in Huzhou. Their antimicrobial resistance phenotype and genes, virulence genes, and phylogenetic relationship were analyzed. Salmonella 4,[5],12:i:-, which all belong to ST34, has become the main serotype of Salmonella isolated in Huzhou instead of S. Typhimurium. Notably, we observed a higher incidence of infections among the young population (<5 years old). The 90 Salmonella isolates were mainly resistant to tetracycline (94.4%), ampicillin (72.2%), and trimethoprim/sulfamethoxazole (70.0%), with multidrug resistance (MDR) rates as high as 93.3%. Genome sequencing indicated that these isolates possessed 39 antimicrobial resistance genes and 184 virulence genes. This research enhances our understanding of S. Typhimurium and Salmonella 4,[5],12:i:- infections, which is helpful to guide clinical responses.