Virulence gene profile analysis and pathogenicity phenotypic heterogeneity of Salmonella enterica serovars Typhimurium and Derby in Caenorhabditis elegans.
Salmonella enterica serovars Typhimurium and Derby are globally prevalent zoonotic pathogens that constitute severe threats to public health, animal husbandry, and socioeconomic development, yet comparatively phenotypic and genomic heterogeneity of their natural isolates remains limited. In this study, we comparatively investigated the virulence gene profile and the pathogenicity of 50 Salmonella isolates comprising serovars Typhimurium (S. Typhimurium) and Derby (S. Derby) in Caenorhabditis elegans through comprehensive phenotypic assays, including lifespan analysis, pharyngeal pumping rate quantification, intestinal colonization measurement, and oxidative stress evaluation. Our results demonstrated that infection with both serovars significantly shortened nematode lifespan, suppressed pharyngeal pumping activity relative to the Escherichia coli OP50-fed control group (p < 0.05). Specifically, S. Typhimurium infection reduced the mean lifespan by 13.99%-33.89%, while S. Derby exposure elicited a 21.48%-30.22% decrease in mean lifespan. Based on the median lethal time (LT50), all the tested isolates were categorized into relatively high pathogenicity (LT50 = 7-8 days, n=13), moderate pathogenicity (LT50 = 9 days, n=28), and relatively low pathogenicity (LT50 = 10-11 days, n=9). Serovar-level differences in survival, pumping, and colonization were minimal. However, S. Derby induced significantly higher H2O2 accumulation than S. Typhimurium (p < 0.05). Genomic analysis demonstrated that pegA, pegB, pegC, pegD, staA, staB, staC, staD, staF, staG, steA, steB, steC, steD, steE, and steF were exclusively present in S. Derby isolates but were absent in S. Typhimurium isolates. In contrast, stcA, stcB, stcC, stcD, ratB, sseI/srfH, and sodCI were present in S. Typhimurium isolates but were absent in S. Derby isolates. Collectively, these findings revealed the phenotypic and genomic heterogeneity of S. Typhimurium and S. Derby, which is beneficial for elucidating their pathogenic mechanisms.