C-230. Resistance of Acanthamoeba Cysts to Disinfection in Multiple Contact Lens Solutions

S. P. Johnston, G. S. Visvesvara, R. Sriram, Y. Qvarnstrom, S. Roy;
CDC, Atlanta, GA.

Acanthamoebae are free-living protozoa found in the environment including soil, fresh and brackish water, and hot tubs/Jacuzzis, which can cause Acanthamoeba keratitis (AK), a painful vision-threatening infection of the cornea and fatal granulomatous encephalitis in humans. More than 20 species of Acanthamoeba belonging to morphological groups I, II and III distributed in 16 genotypes have been described. Among these, A. castellanii, A. polyphaga, and A. hatchetti are frequently identified as causing AK. Acanthamoeba possesses a feeding trophozoite stage and a resistant double-walled cyst stage. Improper contact lens (CL) care and contact with non-sterile water while wearing contact lenses are known risk factors for AK. In addition, a recent increase in AK case-reports was associated with the use of Advanced Medical Optics Complete® MoisturePlus™ multipurpose contact lens solution hypothesized to have had insufficient anti-Acanthamoeba activity. We compared the efficacy of 11 different contact lens solutions purchased from stores against cysts of three species (A. castellanii, A. polyphaga, and A. hatchetti) of Acanthamoeba, genotype T4. These species of Acanthamoeba were obtained from a 2007 outbreak involving this organism. Cysts were suspended in ameba saline, and adjusted to yield 100 cysts per 10 µl. Ten µl of this cyst-containing solution was added to one ml of each lens cleaning solution, in triplicate, and incubated at 24°C for 4 or 6 and 24 h. After incubation, the solutions were washed by centrifugation and all but 0.2 ml of the solution aspirated, mixed gently, inoculated on agar plates coated with E. coli, and incubated at 24°C. Plates were examined daily for two weeks with an inverted microscope for the presence of trophozoites and the efficacy of the solutions was scored qualitatively. The data, generated using A. castellanii cysts, suggest that CL solutions containing hydrogen peroxide are more effective at destroying cysts of A. castellanii than others. In solutions containing multipurpose ingredients, trophozoites of A. castellani were observed as early as 4 hours. Efficacy of these solutions against cysts of A. polyphaga and A. hatchetti will also be discussed.