Motility is considered to be a key virulence-associated phenotype which is common for both host-specific as well as broad-host-range Salmonella serovars. Nevertheless, since the body temperature of mammals is 37ºC, but 41-42ºC in avian hosts, we asked if serovars with different host specificity will present altered motility at different temperatures. We compared the motility of two generalist serovars S. Typhimurium (STM) and S. Enteritidis (SEN) with the motility of human-host-specific serovars S. Typhi (STY) and S. Paratyphi A (SPA). Interestingly, while all Salmonella serovars were motile at 37ºC, a dramatic decrease was measured in the motility of STY, and SPA but not in the motility of STM or SEN at 42ºC. RT-PCR of the flagella class I, II and III genes in STM and SPA at 42ºC vs. 37ºC revealed that unlike STM, in SPA, class II and III genes, but not class I, sharply decreased when grown at 42ºC. We show that heterologous expression of the STM chemoreceptor Tar, naturally inactivated in SPA, significantly improved SPA motility and surprisingly also led to a dramatic decrease in invasion of SPA. Additionally we show that deletion of fliC and flhA in SPA and STM dramatically impaired invasion but not adherence to non-phagocytic epithelial cells. Collectively, our results indicate that while the flagella plays an important role in both SPA and STM virulence, SPA motility is highly temperature sensitive compared to STM motility. Together this may contribute to the unique disease manifestation and host specificity of both serovars.
