Deletion of Two Genes in Burkholderia pseudomallei MSHR668 That Target Essential Amino Acids Protect Acutely Infected BALB/c Mice and Promote Long Term Survival

Abstract

Melioidosis is an emerging disease that is caused by the facultative intracellular pathogen <i>Burkholderia pseudomallei</i>. It is intrinsically resistant to many antibiotics and host risk factors play a major role in susceptibility to infection. Currently, there is no human or animal vaccine against melioidosis. In this study, multiple <i>B. pseudomallei</i> MSHR668 deletion mutants were evaluated as live attenuated vaccines in the sensitive BALB/c mouse model of melioidosis. The most efficacious vaccines after an intraperitoneal challenge with 50-fold over the 50% median lethal dose (MLD₅₀) with <i>B. pseudomallei</i> K96243 were 668 Δ<i>hisF</i> and 668 Δ<i>ilvI</i>. Both vaccines completely protected mice in the acute phase of infection and showed significant protection (50% survivors) during the chronic phase of infection. The spleens of the survivors that were examined were sterile. Splenocytes from mice vaccinated with 668 Δ<i>hisF</i> and 668 Δ<i>ilvI</i> expressed higher amounts of IFN-γ after stimulation with <i>B. pseudomallei</i> antigens than splenocytes from mice vaccinated with less protective candidates. Finally, we demonstrate that 668 Δ<i>hisF</i> is nonlethal in immunocompromised NOD/SCID mice. Our results show that 668 Δ<i>hisF</i> and 668 Δ<i>ilvI</i> provide protective cell-mediated immune responses in the acute phase of infection and promote long term survival in the sensitive BALB/c mouse model of melioidosis.