A capsular vaccine candidate for non-typhoidal Salmonella

Abstract

Salmonella infections remain one of the most common food borne diseases worldwide. Gastroenteritis, which can be caused by many non-typhoidal Salmonella (NTS) serovars, is relatively common in North America. One of the main risk factors of NTS gastroenteritis is travel to endemic areas in the developing world. The current treatment of NTS infections with antibiotics is reserved for severe cases. A growing concern with antibiotic use is that clinical isolates are becoming drug resistant. Although most NTS infections are self-limiting in nature, the burden on the body and recovery can take several months. Thus, it is vital to prevent NTS infections rather than solely rely on treatment. We have previously discovered two novel surface associated polysaccharides in Salmonella: O-Antigen capsule and X-factor. Not only O-Antigen Capsule is considered a common surface antigen, but its’ genes were found to be expressed during in vivo infections in mice. Such an antigen would be a suitable candidate in developing a vaccine against Salmonella induced gastroenteritis. The goal of this research was to evaluate the use of O-Antigen capsule to develop a traveler’s vaccine for NTS associated gastroenteritis. Results and Conclusions: We have developed a purification protocol and purified the capsule and X-factor from Salmonella Typhimurium, Enteritidis, and Heidelberg. Lipopolysaccharide (LPS) was co-isolated with O-Antigen capsule, but removed using Triton extraction. Salmonella LPS is strain-specific and an adaptive immune response against LPS will not provide cross-protection. We generated specific immune sera in rabbits to recognize O-Antigen capsule and X-factor produced by Salmonella Typhimurium and Enteritidis. We used a mouse model to determine the immunization dose of O-Antigen capsule and showed that conjugation is necessary to enhance the immune response in mice. To boost capsule production, we analyzed PyihUTSRQPO activity using a luciferase-based reporter system. Deletion of a putative transcriptional repressor (YihW) resulted in over 100-fold increase in PyihUTSRQPO confirming YihW as a repressor. We have also looked at the effect of growth media, temperature, and sugar precursors on PyihUTSRQPO activity, and were able to show that PyihUTSRQPO has highest activity in Tryptone broth at 30oC in the absence of any additional sugars.