Invasion and intracellular survival of Burkholderia cepacia

Burkholderia, cepacia has emerged as an important pulmonary pathogen in imm unocompromised patients and in patients with cystic fibrosis (CF). Little i s known about the virulence factors and pathogenesis of B. cepacia, althoug h the persistent and sometimes invasive infections caused by B. cepacia sug gest that the organism possesses mechanisms for both cellular invasion and evasion of the host immune response. In this study, cultured human cells we re used to analyze the invasion and intracellular survival of B. cepacia J2 315, a highly transmissible clinical isolate responsible for morbidity and mortality in CF patients. Quantitative invasion and intracellular growth as says demonstrated that B. cepacia J2315 was able to enter, survive, and rep licate intracellularly in U937-derived macrophages and A549 pulmonary epith elial cells. Transmission electron microscopy of infected macrophages confi rmed the presence of intracellular B. cepacia and showed that intracellular bacteria mere contained within membrane-bound vacuoles, An environmental i solate of B. cepacia, strain J2540, was also examined for its ability to in vade and survive intracellularly in cultured human cells. J2540 entered cul tured macrophages with an invasion frequency similar to that of the clinica l strain, but it was less invasive than the clinical strain in epithelial c ells. In marked contrast to the clinical strain, the environmental isolate was unable to survive or replicate intracellularly in either cultured macro phages or epithelial cells. Invasion and intracellular survival may play im portant roles in the ability of virulent strains of B. cepacia to evade the host immune response and cause persistent infections in CF patients.