Functional analysis of the type III secretion apparatus, bsaQ operon from Burkholderia pseudomallei

Burkholderia pseudomallei is the etiological agent of melioidosis in humans. Infection is acquired by inhalation or skin penetration. The most severe form leads to death in approximately 50% of septicemic patients despite optimal antibiotic therapy. No vaccine currently exists against the disease. A B. pseudomallei strain carrying a polar mutation in the bsaQ gene, encoding the structural component of the TTSS, was constructed. Mutation of bsaQ caused a profound effect on the secretion of BopE effector protein into culture supernatants indicating that the Bsa type III secretion apparatus was required for protein secretion. The B. pseudomallei bsaQ polar mutant exhibited decreased plaque formation, bacterial invasion efficiency into non‐phagocytic cells and multinucleated giant cell (MNGC) formation in macrophage cell line. Intracellular localization of the B. pseudomallei mutant strain in the infected host cell relative to lysosome associated membrane glycoprotein‐1 (LAMP‐1) containing vesicles revealed that the bsaQ polar mutant had a delayed ability to escape from the vacuoles of macrophages. Therefore, the defect in MNGC formation might have resulted from delayed escape of the bsaQ mutant from the phagocyte vacuole. This study also demonstrated the importance of the BsaQ type III secretion apparatus in B. pseudomallei entry into host cells. This work was supported by the Thailand Research Fund & Siriraj Grant for Research Development and Medical Education.