Roles of the crp and sipB genes of Salmonella enterica serovar Typhimurium in protective efficacy and immune responses to vaccination in mice.

Salmonella enterica serovar Typhimurium has a wide host range and is capable of causing infections ranging from severe gastroenteritis to systemic infection in humans. To determine if attenuated S. Typhimurium strains can serve as safe and effective oral vaccines to prevent typhoid fever, the biologic characteristics of crp and sipB deletion mutants were evaluated. Previous studies had found that the crp and sipB genes are related to Salmonella pathogenicity. In this study, cytotoxicity, protective efficacy, and immune responses of the host were analyzed. Our previous data had shown a significance decrease in virulence for the crp and sipB mutants compared with a wild-type strain. The current study confirmed this finding in HeLa cells and showed that the crp mutant was significantly less cytotoxic (P < 0.05) than the sipB mutant. Mice vaccinated with the crp mutant showed significantly better protection after challenge with the wild-type strain (P < 0.05) and significantly greater responses in serum IgG (P < 0.01) and secretory IgA (P < 0.05) compared with the mice vaccinated with the sipB mutant (P < 0.05). Our results indicate that the crp mutant has the potential to be a vaccine candidate and is safe in mice.