ABSTRACT
The superiority of live attenuated vaccines in systemic salmonellosis has been proven over killed and subunit vaccines, because of its ability to induce protective cell mediated immunity by CD8+ T cells. A live attenuated Salmonella enterica serovar Typhimurium vaccine has been developed by systematic site directed deletion of the pmrG-HM-D chromosomal genomic loci. This gene confers involved in antimicrobial peptide resistance and is involved in LPS modification, both of which are the major immune evasive mechanisms in Salmonella. The efficacy of the newly developed strain in inducing protection against mortality after challenge with the virulent wild type Salmonella typhimurium 12023 was evaluated in mice model of typhoid fever. Animals were immunized and then boosted on days 7 and 14. Following challenge with virulent S. typhimurium 12023, organ burden and mortality of vaccinated mice were less compared to non-immunized controls. The vaccine strain also induced elevated CD8+ T cells in the vaccinated mice. This multiple mutant vaccine candidate appears to be safe for use in pregnant mice and provides a model for the development of live vaccine candidates against naturally occurring salmonellosis and typhoid fever.
