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T. K. Beattie, A. Tomlinson, D. V. Seal; Efficacy of Complete MoisturePlus Against Acanthamoeba. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4843. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
In 2007 Complete MoisturePlus (CMP), produced by AMO, was voluntarily withdrawn from the market as the Centers for Disease Control and Prevention had indicated a possible increased risk of Acanthameoba keratitis associated with this product. The current study was undertaken to evaluate the efficacy of CMP against Acanthamoeba castellanii trophozoites and cysts using a Most Probable Number (MPN) method to enumerate the organism.
Trophozoites or cysts were inoculated into CMP (active ingredient 0.0001% PHMB) and a control solution (0.9% Amoebal Saline). Samples, taken after 0, 1, 2, 4, 6 and 24h exposure, were neutralised in DE broth prior to dilution in amoebal saline. Five x 1ml, 5 x 0.1ml and 5 x 0.01ml aliquots of the dilutions were inoculated onto non-nutrient agar plates seeded with heat killed bacteria. Plates were incubated at 32ºC for 7-14 days and examined daily for viable amoebae. Results were entered into a MPN statistical table to determine the MPN of amoebae. Experiments were run in triplicate for cysts and trophozoites.
After the manufacturer’s minimum recommended disinfection time (MMRDT) of 4h CMP reduced trophozoite numbers by 3 log, with total kill (log reduction of 3.86) achieved by 6h. Against cysts CMP achieved a 0.55 log reduction by the MMRDT, with a 2 log reduction produced after 24h exposure.
Previous studies by this group have shown little amoebal efficacy during the MMRDT from multipurpose solutions (MPS), including the original Complete (CPL) solution, that contained 0.0001% PHMB; the exception being ReNu Multiplus (RNM) which produced a >3 log reduction in trophozoite numbers. In the current study CMP has shown similar efficacy against trophozoites over the MMRDT as previously shown by RNM. Against cysts MPS containing 0.0001% PHMB, including both CPL and CMP, have been shown to have little effect over MMRDT. However after 24h exposure CMP produced a 2 log reduction in cyst numbers, as compared with a 1 log reduction shown previously by CPL; RNM achieved a >3 log reduction during the same time period. CMP has been shown to have increased efficacy compared to CPL and other MPS containing 0.0001% PHMB. Efficacy was however less than that found with RMP. Issues surrounding the efficacy of MPS against Acanthamoeba could be resolved by the introduction of standardised efficacy testing against Acanthamoeba in FDA approval requirements, using a simple enumeration technique such as the current MPN method, prior to release to the market.
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