Attenuated Virulence and Protective Efficacy of a Vaccine with Multiple Mutated Salmonella enterica Serovar Typhimurium in Mouse

Salmonella typhimurium is the causative agent of bacterial gastroenteritis in human via livestock products. S. typhimurium mutants (ST Delta 4 and ST Delta 5) deleted the hmpA, rpoS, ssrAB, aroA and ppk genes were constructed and, attenuated virulence and protective efficacy of the multiple mutants were evaluated in mice as a novel vaccine candidate. In the virulence test, CFUs of ST Delta 4 (hmpA, rpoS, ssrAB, and aroA) and ST Delta 5 recovered from the liver and spleen of the mice were highly decreased at the range of 2.40 to 5.51 logs for 15 days postinfection. The changes of organ/body weight ratios in mice were also showed same trends as the changes of CFUs in virulence test. In the protection test, CFUs of ST Delta 4 and ST Delta 5 recovered from the organs in mice were highly decreased compared to non-vaccination group. The Polyphospate kinase (ppk) gene was not associated with protective efficacy but attenuated virulence in S. typhimurium mutant. Our results indicated that ST Delta 4 and ST Delta 5 firstly developed in this study showed highly attenuated virulence and protective efficacy. This work shows that S. typhimurium mutant deleted the multiple genes provide a basis for further development of a novel vaccine.