Abstract
Purpose: :
Acanthamoeba Keratitis (AK) is a rare, sight-threatening contact lens associated infection caused by Acanthamoeba protozoa. Withdrawal of a multi-purpose lens disinfection solution in 2007 due to an association with AK has been hypothesized to be related to an encystment promoting effect of the propylene glycol demulcent. To assess the potential relevance of encystment measurements in hydrogen peroxide systems, existing peroxide disinfection systems as well as a novel demulcent-containing peroxide solution were evaluated for encystment effects.
Methods: :
A. castellanii ATCC 50370 trophozoites were cultured in antibiotic-free AC6 medium, treated with test solutions (novel peroxide, Clear Care, AOSEPT, and Oxysept) in neutralizing lens cases for 20 - 24 hr, and evaluated for encystment using bright field and fluorescent microscopy plus Calcofluor White staining. Separately, A. castellanii trophozoites were also treated for 4, 6, or 24 hr in neutralizing lens cases and the surviving trophozoites were enumerated by axenic outgrowth plus Spearman-Karber most probable number computations to calculate log reduction values.
Results: :
Encystment rates for all test solutions were ≤ 1.6% compared to the positive control which caused ≥ 80% trophozoite encystment. When the novel peroxide solution and the Clear Care comparator solution were tested for stand-alone biocidal activity against trophozoites, both solutions showed little or no recovery of live amoeba (i.e. log reduction values ranged from 3.92 to 4.34 after 4, 6, or 24 hr treatments). Also, no encystment occurred when the novel peroxide solution base formulation was tested in further dose-response experiments ranging from 0 - 3 % hydrogen peroxide.
Conclusions: :
A novel one-step peroxide disinfecting solution and three one-step comparator peroxide solutions showed no evidence for encystment effects, suggesting that previously reported encystment effects for a MPS product are not applicable to peroxide-based solutions, regardless of the presence or absence of an ophthalmic demulcent in novel as well as in comparator peroxide solutions.
Keywords: Acanthamoeba • keratitis • contact lens