Burkholderia cepacia is resistant to the antimicrobial activity of airway epithelial cells

Abstract

There has been much interest recently in the antimicrobial properties of cationic peptides called beta-defensins from epithelial cells. Human beta-defensin (hBD)-1 and -2 have been particularly implicated in cystic fibrosis (CF) patients, where their inhibition by high salt concentrations may explain in part the susceptibility of the CF lung to bacterial infection. In this work, we have employed a simple co-culture system using the 16-HBE human bronchial epithelial cell line to assess growth inhibitory activity against Pseudomonas aeruginosa and Burkholderia cepacia. In medium alone, P. aeruginosa proliferated more than 100,000-fold, whereas in the presence of 16-HBE cells or 16-HBE-conditioned medium, bacterial proliferation was less than 100-fold. Raising the salt concentration of cell-free 16-HBE conditioned medium to approximately 200 mM significantly reduced this growth inhibitory activity. In contrast, there was no evidence of epithelial-derived growth inhibitory activity against two strains of B. cepacia. RT-PCR analysis indicated expression of the hBD-2 mRNA in 16-HBE cells, but not hBD-1. These data demonstrate for the first time that B. cepacia is resistant to epithelial-derived antimicrobial substances and argue against them being important in the defense against this organism in the lung.