PSEUDOMONAS-AERUGINOSA INVADES CORNEAL EPITHELIAL-CELLS DURING EXPERIMENTAL-INFECTION

Pseudomonas aeruginosa is considered an extracellular pathogen. Using assays to determine intracellular survival in the presence of gentamic in, we have demonstrated that some strains of P. aeruginosa are able t o invade corneal cells during experimental bacterial keratitis in mice . Although intracellular bacteria were detectable 15 min after inocula tion, the number of intracellular bacteria increased in a time-depende nt manner over a 24-h period. Levels of invasion were similar when bac teria were grown as a biofilm on solid medium and when they were groan in suspension. Intracellular bacteria survived in vitro for at least 24 h, although only minimal bacterial multiplication within cells was observed. P. aeruginosa PAK and Escherichia coli HB101 did not cause d isease in this model and were not isolated from corneas after 24 h eve n when an inoculum of 10(8) CFU was applied. Transmission electron mic roscopy of corneal epithelium from eyes infected for 8 h revealed that intracellular bacteria were present within membrane-bound vacuoles, w hich suggests that bacterial entry was an endocytic process. At 24 h, the observation of many bacteria free in the cytoplasm indicated that P. aeruginosa was able to escape the endocytic vacuole. The ability of some P. aeruginosa strains to invade corneal epithelial cells may con tribute to the pathogenesis or to the progression of disease, since in tracellular bacteria can evade host immune effecters and antibiotics c ommonly used to treat infection.