Amoebicidal activity of multipurpose contact lens solutions.

Purpose: To compare the amoebicidal activity of two commercially available multipurpose contact lens care systems, by using cyst and trophozoite growth of two strains each of Acanthamoeba castellanii and Acanthamoeba polyphaga.

Methods: Trophozoites and cysts of Acanthamoeba species, isolated from corneal ulcers and an ATCC strain, were exposed to two commonly used multipurpose solutions and a saline control for 4 or 6 hours at ambient temperature. After neutralization of the disinfecting solution, track forming units were enumerated on Escherichia coli-seeded nutrient agar plates.

Results: There were significant differences (P<0.01) between solutions, strains, and cysts or trophozoites, but not between the different periods. Solution 2, containing polyquaternium-1 and myristamidopropyl dimethylamine (among other ingredients), gave greater mean log reductions than did solution 1, containing polyaminopropyl biguanide and poloxamine (among other ingredients). Both solutions generally reduced more trophozoites than cysts.

Conclusions: The multipurpose solution containing polyquaternium-1 and myristamidopropyl dimethylamine reduced more cysts and trophozoites than did the alternative solution tested. Because there were differences in the effect of the multipurpose solutions on strains, it is recommended that more than one strain or species of Acanthamoeba be tested to determine efficacy of disinfecting solutions. The lack of difference between disinfection times may indicate that 4 hours could be considered as an adequate disinfecting time to ensure sufficient kill of Acanthamoeba species.