Differential gene expression profiles of lung epithelial cells exposed to Burkholderia pseudomallei and Burkholderia thailandensis during the initial phase of infection.

Burkholderia pseudomallei is the causative agent of melioidosis, and its infection usually affects patients' lungs. The organism is a facultative intracellular Gram-negative bacillus commonly found in soil and water in endemic tropical regions. Another closely related Burkholderia species found in soil and water is B. thailandensis. This bacterium is a non-pathogenic environmental saprophyte. B. pseudomallei is considerably more efficient than B. thailandensis in host cell invasion and adherence. A previous study by our group demonstrated that after successfully invading cells, there was no difference in the ability to survive and to replicate between both Burkholderia species in cultured A549 human lung epithelial cells. In this study, Human Affymetrix GeneChips were used to identify the difference in gene expression profiles of A549 cells after a 2-h exposure to B. pseudomallei and B. thailandensis. A total of 280 of 22,283 genes were expressed at higher levels in the B. pseudomallei-infected cells than in the B. thailandensis-infected cells, while 280 genes were expressed at lower levels in the B. pseudomallei-infected cells. Approximately 9% of these genes were involved in immune response and apoptosis. Those genes were further selected for gene expression analysis using reverse transcription PCR and/or real-time RT-PCR. The results of RT-PCR and real-time RT-PCR are in accordance with data from the microarray data in that bcl2 gene expression in the B. pseudomallei-infected cells was 2-fold higher than the level in the B. thailandensis-infected cells even though no apoptosis was seen in the infected cells. The levels of E-selectin, ICAM-1, IL-11, IRF-1, IL-6, IL-1beta and LIF genes expression in the B. pseudomallei-infected cells were 1.5-5 times lower than in the B. thailandensis-infected cells. However, both species stimulated the same level of IL-8 production from the tested epithelial cell line, and no difference in the ratio of adherent polymorphonuclear cells (PMNs) to infected A549 cells of both species was observed. Taken together, our results suggest that B. pseudomallei manipulates host response in favor of its survival in the host cell, which may explain the more virulent characteristics of B. pseudomallei when compared with B. thailandensis.