Burkholderia pseudomallei is the causative agent of melioidosis, a dis
ease being increasingly recognized as an important cause of morbidity
and mortality in many regions of the world. Several features of melioi
dosis suggest that B. pseudomallei is a facultative intracellular path
ogen. This study was designed to assess the ability of B. pseudomallei
to invade and survive in eukaryotic cells. We have shown that B. pseu
domallei has the capacity to invade cultured cell lines, including HeL
a, CHO, A549, and Vero cells. We have demonstrated intracellular survi
val of B. pseudomallei in professional phagocytic cells, including rat
alveolar macrophages, B. pseudomallei was localized inside vacuoles i
n human monocyte-like U937 cells, a histiocytic lymphoma cell line wit
h phagocytic properties. Additionally, electron microscopic visualizat
ion of B. pseudomallei-infected HeLa cells and polymorphonuclear leuko
cytes confirmed the presence of intracellular bacteria within membrane
-bound vacuoles. B. pseudomallei was found to be resistant to the cati
onic peptide protamine and to purified human defensin HNP-1.