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A. Lam, S. Kilvington; Screening Method for Efficacy Testing of Contact Lens Disinfectants Against Acanthamoeba. Invest. Ophthalmol. Vis. Sci. 2009;50(13):6361.
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Unlike the requirements for bacteria and fungi, no standard exists for efficacy of contact lens disinfectant (CLD) solutions against Acanthamoeba. As such, a variety of test methods have been reported that present frequently differing results. Here we report a simple test method for screening the efficacy of CLDs against Acanthamoeba spp.
A. castellanii (50370) and A, polyphaga (1501/3g) trophozoites and cysts were tested. 5 ml of test solution (x3) was challenged with 100 trophozoites or cysts. After 6 hr, 5 ml of neutraliser containing E. coli was added and the tubes centrifuged at 1000 x g for 10 min. The cell pellet was resuspended in a few drops of supernatant and inoculated on to the well of a 12 place microtitre plate containing non-nutrient agar for incubation at 28ºC for 14 days. Surviving trophozoites, or excysted trophozoites, feed and replicate on the E. coli lawn and are seen microscopically.
Variation in test solution efficacy against trophozoites of both species was observed, even within those based on the same concentration of PHMB (Table). No MPS achieved total kill of cyst inoculum. Only the 1-step peroxide killed trophozoites and cysts of both species. Trophozoite efficacy of MPS-7 was lost on depletion by overnight incubation with PureVision lenses.
The assay enables Acanthamoeba CLD efficacy to be assessed. It lacks the sensitivity of a time kill assay as it relies on the total inoculum kill (100 organisms) to give a 2-log10 or 99% reduction. However, as a screening method the assay is simple to perform and can be easily modified to assess experimental variables such as challenge inoculum size, contact time, choice of species and strain and method of cyst production. Loss of anti-acanthamoebal activity through contact lens depletion would appear to be a potentially significant factor.
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