Genome analysis and virulence gene expression profile of a multi drug resistant Salmonella enterica serovar Typhimurium ms202

In India, multi-drug resistance in Salmonella enterica serovar Typhimurium poses a significant health threat. Indeed, S. Typhimurium has remained unknown for a large portion of its genome associated with various physiological functions including mechanism of drug resistance and virulence. The whole-genome sequence of a Salmonella strain obtained from feces of a patient with gastroenteritis in Odisha, India, was analyzed for understanding the disease association and underlying virulence mechanisms.

The de novo assembly yielded 17 contigs and showed 99.9% similarity to S. enterica sub sp enterica strain LT2 and S. enteric subsp salamae strain DSM 9220. S. Typhimurium ms202 strain constitutes six known Salmonella pathogenicity islands and nine different phages. The comparative interpretation of pathogenic islands displayed the genes contained in SPI-1 and SPI-2 to be highly conserved. We identified sit ABCD cluster regulatory cascade in SPI-1. Multiple antimicrobial resistance genes were identified that directly implies antibiotic-resistant phenotype. Notably, seven unique genes were identified as "acquired antibiotic resistance". These data suggest that virulence in S. enterica Typhimurium ms202 is associated with SPI-1 and SPI-2. Further, we found several virulent genes encoding SPI regions belonging to type III secretion systems (T3SS) of bacteria were significantly upregulated in ms202 compared to control LT2. Moreover, all these genes were significantly downregulated in S. enterica Typhimurium ms202 as compared to control LT2 on adding Mn²⁺ exogenously.