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Monica J Crary, Rhonda Walters, Jorge Silva, Manal M Gabriel, Stephen Paul Shannon; Evaluation of Acanthamoeba encystment against OPTI-FREE contact lens care products. Invest. Ophthalmol. Vis. Sci. 2016;57(12):1451.
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© ARVO (1962-2015); The Authors (2016-present)
Contact lens solutions with low antimicrobial activity against Acanthamoeba trophozoites may induce encystment during lens storage. The new issued ISO standard 19045 ‘Method for evaluating Acanthamoeba encystment by Contact Lens Care Products’ assesses the intrinsic encystment properties of contact lens disinfecting solutions. The purpose of this study is to evaluate the promotion of Acanthamoeba encystment by OPTI-FREE products using a modified assay based on ISO 19045.
To determine the induction of encystment by OPTI-FREE RepleniSH, OPTI-FREE Express, and OPTI-FREE PureMoist, each solution was inoculated with two strains of Acanthamoeba trophozoites (ATCC 50370 and 30461) at a density of 105 cells/mL per ISO 19045. Acanthamoeba was also inoculated into Ringer’s solution at Time 0 to determine initial cyst concentration. At 0 and 24 hours, encystment was determined by calculating total cell density and cyst density using both a hemocytometer and a flow cytometer. Prior to calculating cyst density, each solution was treated with 5% SDS for 5 minutes to remove immature cysts and trophozoites. Each solution was washed with Ringer’s solution to remove SDS and either enumerated using a flow cytometer or treated with calcofluor white to stain the cellulose wall of the cyst and counted with a hemocytometer. The percent encystment was determined for each condition.
Initial cyst concentrations were < 0.5% for both Acanthamoeba strains. Strong correlation between the flow cytometer and hemocytometer counts was observed. The flow cytometer had a lower limit of quantification (101) than the hemocytometer (103). For OPTI-FREE RepleniSH, OPTI-FREE Express, and OPTI-FREE PureMoist, Acanthamoeba ATCC 50370 and ATCC 30461 had <1.0% encystment with both the hemocytometer and flow cytometer.
Evaluating the encystment of Acanthamoeba in a contact lens disinfecting solution is important to determine the risk of exposing users to drug and biocide resistant cysts during normal contact lens wear. OPTI-FREE RepleniSH, OPTI-FREE Express and OPTI-FREE PureMoist have sufficient antimicrobial activity against Acanthamoeba trophozoites and do not induce encystment.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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