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Megan E. Shoff, Victoria Hitchins; Important Variables When Using Acanthamoeba to Evaluate Contact Lens Solutions. Invest. Ophthalmol. Vis. Sci. 2011;52(14):5828.
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To investigate the important parameters in the culture and encystment of Acanthamoeba castallanii spp. when testing for biocidal efficacy of multipurpose solution (MPS).
Two strains of A. castallanii were evaluated, one from ATCC (50370) and one from the Centers for Disease Control and Prevention (CDC-V568). Both were grown using two different methods: xenically on non-nutrient amoeba saline agar seeded with Enterobacter aerogenes and axenically in ATCC growth medium PYG-712. Amoebae from both growth methods and both strains were treated with four different MPS as trophozoites. Further, four encystment methods were employed against both strains and both growth mediums. Cysts were subsequently treated with the four MPS solutions containing different disinfectants. Aliquots were removed and tested for survivors at 50% and 100% of recommended treatment times and at 24h. Experiments were run in triplicate, and controls using amoeba saline were run with each group of experiments in order to verify inoculum. A 5-tube most probable number method was used to enumerate the survivors and to determine the log kills.
As expected, trophozoites were more easily killed than cysts. There was a marked difference in effectiveness between solutions, which varied with growth conditions and encystment method. Growth medium affected survival in some cases. Further, there was a significant difference in cyst survival dependent on encystment method. The strain used was less of a factor in trophozoite resistance to MPS. However, cyst resistance to MPS was dependent on which strain was used.
When designing a protocol involving Acanthamoeba, many parameters must be evaluated for significance. It is important to use the appropriate protocol for efficacy testing of MPS against Acanthamoeba as susceptibility to biocides varies with growth media, strain and methods for encystation.
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