Purpose: To investigate the relative efficacy of Japanese commercial soft contact lens disinfectant solutions against Acanthamoeba trophozoites and cysts.
Materials and methods: Eight types of multipurpose solution (MPS), two types of hydrogen peroxide solution, and one povidone-iodine solution were evaluated to determine their effect against Acanthamoeba trophozoites and cysts (ATCC 50514). Acanthamoeba cysts were cultured in encystment medium for either 1 or 2 weeks (1 and 2-week-old cysts). The trophozoites and cysts were treated with each disinfectant solution for 0, 2, 4, 8, or 24 h. After performing four tenfold serial dilutions of each test solution, dilutions were cultured for 10 days. The number of surviving organisms was calculated using the trimmed Spearman-Karber method.
Results: Among the MPS tested, only four were effective against trophozoites after treatment for 4 h, and none was effective against 2-week-old cysts. Hydrogen peroxide had a significant effect on trophozoites and 1-week-old cysts, but not on 2-week-old cysts. In contrast, povidone-iodine caused a 2.6 log reduction in 2-week-old cysts.
Conclusions: MPS were found to have limited efficacy against trophozoites and no efficacy against 2-week-old cysts. Only povidone-iodine had any efficacy against 2-week-old cysts.