C. Lakkis et Smj. Fleiszig, Resistance of Pseudomonas aeruginosa isolates to hydrogel contact lens disinfection correlates with cytotoxic activity, J CLIN MICR, 39(4), 2001, pp. 1477-1486
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.