Invasive strains of Pseudomonas aeruginosa are able to cause epithelial cell cytotoxicity that is dependent on bacterial cell density.

The purpose of this study was to investigate the hypothesis that quorum-sensing systems are involved in the ability of invasive Pseudomonas aeruginosa strains to cause corneal epithelial cell death. Two invasive strains, 6294 and PAOI, were co-cultured with human corneal epithelial cells at different bacterial concentrations (10(5), 10(7) and 10(9) CFU/mL). Cytotoxicity was measured using a cytotoxicity assay kit. The levels of autoinducer in the supernatant were examined using a reporter strain of Agrobacterium tumefaciens (A136). Protease production was also monitored. Cytotoxicity of both strains was dependent on bacterial density; a moderate to high concentration of bacterial cells (10(7) and 10(9) CFU/mL) caused 70% to 94% loss of cell variability. Cytotoxicity was significantly correlated with enhanced autoinducer and protease production (r>0.95, P<0.05). These results indicate that the invasive strains regulate the production of virulence factors and, in turn, induce chronic dose-related cytotoxicity.