Similar Virulence Gene Repertoires but Distinct Stress Tolerance and Pathogenicity-Associated Phenotypes in Representative Salmonella Typhimurium ST19 and ST213 Strains from Mexico

Foodborne illnesses caused by Salmonella Typhimurium remain a major public health concern worldwide. Although ST19 has historically been a dominant lineage within this serotype, ST213 has become increasingly prevalent in Mexico. The biological factors underlying this epidemiological shift remain incompletely understood. In this study, we compared virulence-associated gene repertoires and stress-related phenotypes in representative S. Typhimurium ST19 and ST213 strains with distinct virulotypes (VTs). Comparative genomic analysis identified 119 virulence-associated genes distributed across 26 VTs, with most genes broadly conserved between genotypes. Representative strains were evaluated under simulated gastrointestinal tract (GIT) stress conditions, in post-stress recovery assays, and in a Caenorhabditis elegans infection model. Under the experimental conditions evaluated, the representative ST213 strains SAL109 (VT1), SAL115 (VT1), and SAL016 (VT12) tended to show higher persistence under host-associated stress conditions and greater intestinal colonization capacity in C. elegans than the ST19 strain SAL004 (VT23). However, strains sharing the same VT did not necessarily exhibit similar phenotypes, indicating that virulence-associated gene repertoires alone do not fully explain stress tolerance or host colonization behavior. Overall, these findings highlight phenotypic variability among strains with similar virulence gene content and support the importance of integrating genomic and phenotypic approaches to better understand the biology of emerging S. Typhimurium lineages.