Resistance of Pseudomonas aeruginosa isolates to hydrogel contact lens disinfection correlates with cytotoxic activity

One of the most common pathogens in infection of hydrogel contact lens wear ers is Pseudomonas aeruginosa, which can gain access to the eye via contami nation of the lens, lens case, and lens care solutions. Only one strain per species Is used in current regulatory testing for the marketing of chemica l contact lens disinfectants. The aim of this study was to determine whethe r P. aeruginosa strains vary in their susceptibility to hydrogel contact le ns disinfectants. A method for rapidly screening bacterial susceptibility t o contact lens disinfectants was developed, based on measurement of the MIC . The susceptibility of 35 P. aeruginosa isolates to two chemical disinfect ants was found to vary among strains. MICs ranged from 6.25 to 100% for bot h disinfectants at 37 degreesC, and a number of strains were not inhibited by a 100% disinfectant concentration in the lens case environment at room t emperature (22 degreesC). Resistance to disinfection appeared to be an inhe rent rather than acquired trait, since some resistant strains had been isol ated prior to the introduction of the disinfectants and some susceptible F, aeruginosa strains could not be made more resistant by repeated disinfecta nt exposure, A number of P. aeruginosa strains which were comparatively mor e resistant to short-term disinfectant exposure also demonstrated the abili ty to grow to levels above the initial inoculum in one chemical disinfectan t after long-term (24 to 48 h) disinfectant exposure. Resistance was correl ated with acute cytotoxic activity toward corneal epithelial cells and with exsA, which encodes a protein that regulates cytotoxicity via a complex ty pe III secretion system. These results suggest that chemical disinfection s olutions may select for contamination with cytotoxic strains. Further inves tigation of the mechanisms and factors responsible for resistance may also lead to strategies for reducing adverse responses to contact lens wear.