Burkholderia pseudomallei is the cause of melioidosis, an endemic disease in South-East Asia and Northern Australia, with a mortality rate of ~15%. With rising levels of antibiotic resistance and a lack of effective treatment for melioidosis, novel medical countermeasures are needed. Cyclophilins are enzymes which catalyse the cis-to-trans isoform change of xaa-proline bonds, a rate limiting step in protein folding. Cyclophilins have been associated with virulence in intracellular bacteria. As they are highly conserved, cyclophilins present as anti-virulence targets for many pathogenic bacteria, including B. pseudomallei, which encodes two cyclophilin genes, ppiA and ppiB. This study investigates the role of cyclophilins in B. pseudomallei by constructing in-frame deletion mutants; B.psΔppiA, B.psΔppiB and B.psΔppiAppiB.
B.psΔppiA and B.psΔppiB were impaired in biofilm formation with B.psΔppiA showing a 60% reduction and B.psΔppiB showing an 80% reduction in biofilm, suggesting that B.psΔppiA and B.psΔppiB play different roles in the cell. A 25% decrease in motility was also seen with B.psΔppiA and B.psΔppiB. B.psΔppiAppiB exhibits no motility defect, the reason for this is currently being investigated. Gross morphological changes are also observed by Transmission Electron Microscopy, with B.psΔppiA displaying an aberrant outer membrane structure. B.psΔppiA, B.psΔppiB and B.psΔppiAppiB display an increased susceptibility to oxidative stress, reflected in reduced survival in macrophages. B.psΔppiA and B.psΔppiAppiB show a 50% reduction in bacterial numbers over the initial 9 hours post-infection. B.psΔppiB shows greater attenuation in macrophages with initial counts similar to that of B.psΔppiA, but intracellular counts decrease over 9 hours. In vivo studies using mouse infection models is currently underway to determine the effect of cyclophilins on disease. These results suggest that cyclophilins ppiA and ppiB play an important role in B. pseudomallei virulence.