FIGURE 1.

Molecular bases for differences between typhoidal and NTS serovars. (A) Typhoidal serovars possess several inactive/degraded genes compared to NTS serovars such as genes for chemotaxis, adhesion, and anaerobic metabolism. (B) Both typhoidal and NTS serovars possess unique virulence factors. For example, some S. Typhi strains express Vi capsule that reduces TLR-dependent IL-8 production in the intestinal mucosa. However, while the Vi capsule plays a role in typhoid fever manifestation, it is not necessary as it is absent from other typhoidal serovars and Vi-negative mutants of S. Typhi are still able to cause a typhoid-like illness in humans. (C) In contrast to typhoidal serovars, NTS cause severe intestinal inflammation. NTS serovars have evolved to utilize inflammation-derived metabolites (e.g., nitrate and tetrathionate), thereby enhancing their growth in the inflamed intestine. Typhoidal serovars have lost the ability to benefit from inflammation-derived metabolites and disseminate to systemic sites to a much greater extent.