Antibiotic treatment does not necessarily prevent pseudomonas aervginosa induced cell damage

Purpose. Some P. aeruginosa isolates can invade epithelial cells in vivo. After invasion, bacteria break out of their endosome and replicate within the cytoplasm. Other bacteria that behave in this manner (Listeria monocytogenes and Shigella flexneri) can spread from cell-to-cell via intracellular compartments, and thereby form plaques of dead cells. The purpose of this study was to investigate the fate of intracellutar P. aeruginosa and their host corneal epithelial cells. Methods. Rabbit corneal epithelial cells were infected with 105 cfu of P. aeruginosa strain 1244, or L. monocytogenes 10403S for 1 h. Control samples were either not inoculated, or were infected with one of two types of bacteria that do not invade corneal epithelial cells (P. aeruginosa strain 6206, Escherichia coli strain HB101). Infected cells were overlaid with 0.6% agarose in tissue culture medium containing 50u,g gentamicin/ml (the MIC of all strains was < 2u.g/ml) and incubated at 37°C. The overlay was shown to kill extracellular bacteria in cell samples within l h using strain 6206. After 3 days, dead and dying cells were visualized by application of 0.16% trypan blue to the agarose surface. Results. Cells that had been inoculated with cither L. monocytogenes 10403S or P. aeruginosa 1244 were completely destroyed by the bacteria. Cells that were not inoculated, or those inoculated with the control strains, survived the 3 day overlay with agarose and gentamicin. Conclusions. Although P. aeruginosa strains that invade cells do not induce acute cell cytotoxicity, these strains can kill epithelial cells after long term exposure; even in the presence of an antibiotic that can kill extracellular bacteria. There are two alternative explanations for these results; 1) cell killing could have resulted from exposure to dead extracellular bacteria, or 2) P. aeruginosa strain 1244 could spread from cell-to-cell and kill without entering the extracellular space. These results show that antibiotic therapy of infected tissues may not prevent destruction of cells by certain strains of P. aeruginosa.