Abstract
While the results of Acanthamoeba testing have been extensively published, laboratories conducting such testing are left to develop their own methods in the absence of a standardized methodology. The wide disparity of methods has resulted in equally inconsistent reported results for contact lens care (CLC) products. This study’s objective was to determine the source of these discrepancies by evaluating basic Acanthamoeba biology and their impact on antimicrobial efficacy testing, including the ability of a recovery method to stimulate a single trophozoite to proliferate. Antimicrobial efficacy testing was conducted using well-published Acanthamoeba strains, storage conditions, and growth-based recovery methods. To identify variables that influence results, test solutions with low Acanthamoeba disinfection rates were utilized to prevent differences from being masked by high log reductions. In addition, single-cell proliferation assays were executed to understand the growth requirements to stimulate trophozoite propagation in two recovery methods. These studies indicated that both nutrient density (>106 CFU) and the length of plate incubation (at least 14 days) could significantly influence the accurate recovery of trophozoites. Together, this study emphasizes the need to understand how Acanthamoeba trophozoites biology can impact test methods to create divergent results.
Highlights
Acanthamoeba keratitis is a blinding eye infection, most often associated with contact lens users and poor contact lens care compliance [1,2,3,4,5]
Previous Acanthamoeba outbreaks have been associated with ineffective anti-Acanthamoeba activity of a contact lens care (CLC) product [21], and for this purpose, it is common for CLC manufacturing companies to highlight their Acanthamoeba efficacy for marketing
We examine the impact of basic Acanthamoeba biology and the potential pitfalls that prevent the development of robust testing methods for evaluating Acanthamoeba trophozoites
Summary
Acanthamoeba keratitis is a blinding eye infection, most often associated with contact lens users and poor contact lens care compliance [1,2,3,4,5]. Acanthamoeba keratitis stories have been widely reported in mainstream news, highlighting high-risk behaviors such as swimming with contact lenses and poor contact lens hygiene [16,17,18,19]. Since 2009, the FDA and other regulatory bodies have been urged to include Acanthamoeba as a standard microorganism to evaluate the antimicrobial efficacy of new contact lens care products [20]. Previous Acanthamoeba outbreaks have been associated with ineffective anti-Acanthamoeba activity of a contact lens care (CLC) product [21], and for this purpose, it is common for CLC manufacturing companies to highlight their Acanthamoeba efficacy for marketing. Other keratitis outbreaks, such as the Fusarium outbreak in 2005, were a result of poor antimicrobial efficacy of CLC products [22]
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