Interaction between Burkholderia pseudomallei and Acanthamoeba species results in coiling phagocytosis, endamebic bacterial survival, and escape

Burkholderia pseudomallei causes melioidosis, a potentially fatal disease w hose clinical outcomes include rapid-onset septicemia and relapsing and del ayed-onset infections. Like other facultative intracellular bacterial patho gens, B. pseudomallei is capable of survival in human phagocytic cells, but unlike mycobacteria, Listeria monocytogenes, and Salmonella serovar Typhim urium, the species has not been reported to survive as an endosymbiont in f ree-living amebae, We investigated the consequences of exposing Acanthamoeb a astronyxis, A. castellani, and A. polyphaga to B. pseudomallei NCTC 10276 in a series of coculture experiments, Bacterial endocytosis was observed i n all three Acanthamoeba species, A more extensive range of cellular intera ctions including bacterial adhesion, incorporation into amebic vacuoles, an d separation was observed with A. astronyxis in timed coculture experiments . Amebic trophozoites containing motile intravacuolar bacilli were found th roughout 72 h of coculture. Confocal microscopy was used to confirm the int racellular location of endamebic B. pseudomallei cells, Transmission electr on microscopy of coculture preparations revealed clusters of intact bacilli in membrane-lined vesicles inside the trophozoite cytoplasm; 5 x 10(2) CFU of bacteria per mi were recovered from lysed amebic trophozoites after 60 min of coculture. Demonstration of an interaction between B. pseudomallei a nd free-living acanthamebae in vitro raises the possibility that a similar interaction in vivo might affect environmental survival of B. pseudomallei and subsequent human exposure. Endamebic passage of B. pseudomallei warrant s further investigation as a potential in vitro model of intracellular B. p seudomallei infection.