Melioidosis is a potentially fatal infection caused by Burkholderia pseudomallei. Treatment of this infection is lengthy and relies on a limited number of antibiotics with recent reports describing isolates resistant to current treatment options. Therefore, the identification of new antibacterial targets is needed to develop new therapies. A potential target is sensitive to lysis D (SlyD), an FK506-binding protein (FKBP) that catalyses the cis-trans isomerisation of proline bonds, a known rate-limiting step in protein folding. SlyD proteins have been shown to play a role in the virulence of several pathogenic bacteria. Disruption of the slyD gene resulted in a 50% reduction in chick intestine colonisation by Salmonella enterica serovar Typhimurium, compared to the parent strain. While in Helicobacter pylori, SlyD is required for the incorporation of nickel by urease, which is essential for acid resistance and survival in the highly acidic gastric environment.
This study investigated the role of slyD in the virulence of B. pseudomallei by constructing an unmarked gene deletion mutant, Bps∆slyD. The complemented strain Bps∆slyD/slyD was also constructed by re-introducing the deleted gene via the plasmid vector pMLBAD. Bps∆slyD was exposed to several stress conditions that it would naturally encounter during infection including oxidative and acidic stress. Bps∆slyD was more susceptible to oxidative stress induced by 1 mM hydrogen peroxide with the Bps∆slyD/slyD able to rescue the phenotype. Furthermore, Bps∆slyD also showed an increased susceptibility to acidic stress when exposed to citrate-phosphate buffer at pH 4, however, this phenotype was not restored with Bps∆slyD/slyD. The ability to infect both macrophage and epithelial cells was significantly reduced in Bps∆slyD, this was restored to wild-type levels in Bps∆slyD/slyD. Additionally, there was a reduction in bacterial-induced cytotoxicity in both cell lines at 24 hrs post-infection with Bps∆slyD as determined by measuring the levels of lactate dehydrogenase. Altogether, these findings demonstrate that deletion of the slyD results in a loss of virulence in B. pseudomallei and is, therefore, a potential target for anti-virulence therapy.