Burkholderia pseudomallei RpoS regulates multinucleated giant cell formation and inducible nitric oxide synthase expression in mouse macrophage cell line (RAW 264.7).

Burkholderia pseudomallei is the causative agent of melioidosis. This bacterium can invade and survive inside the phagocytic and nonphagocytic cells. After internalization, the bacteria can escape from the membrane-bound phagosome into the cytoplasm. Internalised B. pseudomallei can also induce a cell-to-cell fusion, resulting in a multinucleated giant cell (MNGC) formation. In the present study, we demonstrated that B. pseudomallei rpoS null mutant was similar to its wild type parent in its ability to survive and multiply inside the mouse macrophages, but it failed to stimulate MNGC formation. The rpoS mutant was also unable to activate inducible Nitric Oxide Synthase (iNOS) in resting mouse macrophages but in gamma interferon (IFN-gamma)-activated macrophages, the mutant was able to induce significantly higher levels of iNOS and NO when compared with its wild-type counterpart, resulting in a significantly lower number of bacteria inside the infected host cells.