Difference in susceptibility to environmental stressors between Salmonella enterica serovars Typhi & Typhimurium
Embargo Date
2025-02-17
OA Version
Citation
Abstract
Although the enteropathogens S. Typhi and S. Typhimurium share 90% of their genes and utilize similar infection mechanisms, they have different host ranges and cause different pathologies in humans, gastroenteritis and typhoid fever, respectively. Both Salmonella serovars encounter environmental conditions in the gastrointestinal tract that are potentially stressful and are detrimental to their survival. Stressors include the notable fluctuations in pH, the presence of bile salts and reactive oxygen species. Unlike S. Typhi, S. Typhimurium has to also deal with stresses brought forth by an onslaught of the intestinal inflammatory response. As it stands now, it is not fully known whether S. Typhi and S. Typhimurium differ in their ability to respond to these environmental stresses and whether any of these differences are clinically relevant to the diseases they cause.
Serendipitously, in previous studies conducted at our lab, it was found that there was a significant increase in the susceptibility of the Ty2 strain of S. Typhi to a 1% solution of the detergent Triton X-100 in water compared to the SL1344 strain of
S. Typhimurium. Through our study, we were able to show that this decreased viability of Ty2 was a result of the combined effects of the detergent and the hypotonicity of the water. We were also able to show that Ty2 is significantly more sensitive to hydrogen peroxide than SL1344.
The rpoS gene is implicated in the bacterial response to environmental stresses. Previously published studies have established that while the Ty2 strain of S. Typhi carries a frameshift mutation in rpoS, SL1344 has a wild-type copy of the same gene. We hypothesized that the rpoS mutation made Ty2 differentially sensitive to Triton in water and hydrogen peroxide compared to SL1344. In order to test this, we cloned a wild-type copy of the rpoS gene from SL1344 and expressed it in Ty2. We observed that the Ty2 transformant with the functional rpoS had significantly enhanced resistance to both Triton in water and hydrogen peroxide. The results of our study thus indicate that the lack of a functional rpoS renders S. Typhi susceptible to at least 2 different environmental stressors. We will need to conduct further studies in order to substantiate these findings and determine the significance of our observations as it relates to S. Typhi pathogenicity in vivo.