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S. Kilvington, W. Heaselgrave, H. Powell, J. Lally; Physiological Response of Acanthamoeba Trophozoites to Multipurpose Contact Lens Solutions: Aggregation and Resistance to Disinfection. Invest. Ophthalmol. Vis. Sci. 2009;50(13):6360.
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The physiological effect of multipurpose solutions (MPS) on Acanthamoeba is an area of increasing interest. Here, the response of trophozoites during incubation in various MPS was investigated. The observation that certain MPS can cause mass aggregation of trophozoites which may afford protection from disinfection is reported.
MPS (3 ml) in microtitre plates were challenged with 5 x 10^5 A. castellanii (ATCC 50370) trophozoites, incubated at 25ºC and microscopic observations made over time. After 24 hr, sarkosyl (0.25%) was added to lyse trophozoites and any cysts counted. The disinfectant efficacy of selected MPS against trophozoites was also tested.
Trophozoite appearance during MPS incubation is shown in the figure. MPS-1 caused rapid, aggregation of trophozoites (4+). Others induced aggregation to a lesser extent: MPS-3 (2+), MPS-4 (1+) and MPS-2 (0). Depletion of MPS-4 efficacy by Acuvue 2 lenses (MPS-4a) resulted in increased aggregation (3+) and loss of disinfectant efficacy. Addition of EDTA (0.05%) reduced MPS-1 aggregation to 0% at 6 hr. MPS-1 induced slight encystment (3%) compared to other solutions (0%). Addition of propylene glycol (0.5%) to MPS-1 resulted in 15% encystment. MPS-1 was not effective in killing trophozoites.
MPS induced aggregation of trophozoites is a novel finding and may limit the efficacy of MPS disinfectants against Acanthamoeba. Reasons for this phenomenon continue to be investigated but EDTA may be a limiting factor. Physiological effects by MPS on trophozoites such as aggregation, encystment and associated resistance to disinfection reinforces the need for care and consideration when developing contact lens solutions.
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