Prevalence, Antimicrobial Resistance, and Genomic Characterization of Salmonella Typhimurium Isolated in Hengyang, China (2020–2023)

Objective: To determine the prevalence, antimicrobial resistance (AMR) profiles, and genomic characteristics of Salmonella isolates in Hengyang, China, from 2020 to 2023, with a focus on Salmonella Typhimurium. Methods: Salmonella isolates were identified using standard microbiological methods. Salmonella Typhimurium strains underwent antimicrobial susceptibility testing and whole-genome sequencing. Genomic analyses were performed to identify AMR genes, virulence factors, mobile genetic elements, and phylogenetic relationships. Results: Among the 255 Salmonella isolates from food and patient sources, Salmonella Typhimurium was the predominant serotype (82 isolates, 32.16%), primarily represented by sequence types ST34 and ST19. All isolates were susceptible to imipenem , while tetracycline resistance was the most common (80.5%, 66/82). Forty-one resistance genes, spanning eight antimicrobial classes, were identified. ST34 strains carried more resistance genes (38) than ST19 (15). Virulence gene profiles were largely similar between the two lineages, but gogB and shdA were specific to ST34. Among mobile genetic elements, the ColRNAI plasmid was most prevalent, and insertion sequences were ubiquitous. Phylogenetic analysis revealed that ST34 and ST19 strains from Hengyang were interspersed with strains from southern and eastern China. Conclusion: Salmonella Typhimurium ST34 is the dominant multidrug-resistant lineage in Hengyang, characterized by a larger resistome and unique virulence factors. Its close phylogenetic relationship with strains from southern and eastern China, combined with active mobile genetic elements, underscores its role in regional dissemination and adaptive evolution.