Burkholderia pseudomallei induces cell fusion and actin-associated membrane protrusion: a possible mechanism for cell-to-cell spreading

Burkholderia pseudomallei, a facultative intracellular bacterium, is the ca usative agent of a broad spectrum of diseases collectively known as melioid osis. Its ability to survive inside phagocytic and nonphagocytic cells and to induce multinucleated giant cell (MNGC) formation has been demonstrated. This study was designed to assess a possible mechanism(s) leading to this cellular change, using virulent and nonvirulent strains of B. pseudomallei to infect both phagocytic and nonphagocytic cell lines. We demonstrated tha t when the cells were labeled with two different cell markers (CMFDA or CMT MR), mixed, and then infected with B. pseudomallei, direct cell-to-cell fus ion could be observed, leading to MNGC formation. Staining of the infected cells with rhodamine-conjugated phalloidin indicated that immediately after the infection, actin rearrangement into a comet tail appearance occurred, similar to that described earlier for other bacteria. The latter rearrangem ent led to the formation of bacterium-containing, actin-associated membrane protrusions which could lead to a direct cell-to-cell spreading of B. pseu domallei in the infected hosts. Results from 4',6'-diamidine-2-phenylindole dihydrochloride (DAPI) nuclear staining, poly-ADP ribose polymerase cleava ge, staining of infected cells for phosphatidylserine exposure with annexin V. and electrophoresis of the DNA extracted from these infected cells show ed that B. pseudomallei could kill the host cells by inducing apoptosis in both phagocytic and nonphagocytic cells.