Acanthamoeba: An Overview of the Challenges to the Development of a Consensus Methodology of Disinfection Efficacy Testing for Contact Lens Care Products

Abstract

With the increasing incidence of more pathogens that can cause microbial keratitis (MK), it is necessary to periodically reassess disinfection multipurpose solutions testing requirements to ensure that relevant organisms to challenge them are being used. Current testing protocols have included common pathogens such as Pseudomonas aeruginosa, Staphylococcus aureus, Serratia marcescens, Candida albicans, and Fusarium solani but have omitted less common pathogens such as Acanthamoeba. Specifically, Acanthamoeba sp. has recently been identified as a prevalent cause of MK in certain countries. Developing an appropriate protocol for this unique organism presents a challenge, given its two distinct life stages, methods to grow the organism, encystment techniques, and many other parameters that can affect testing outcomes. Therefore, the appropriate combination of these parameters is crucial to developing a protocol that ensures consistent, accurate results. The FDA has recognized the importance of establishing a standardized testing protocol for this pathogen and embarked on research efforts to provide a recommended testing protocol for testing contact lens care products.

Evaluating Alternate Methods of Determining the Antimicrobial Efficacy of Contact Lens Care Products against Acanthamoeba Trophozoites

“…For method development, the two most-commonly used strains of Acanthamoeba trophozoites in CLC product testing (ATCC 50370, ATCC 30461) [8,16] and one more novel strain (ATCC 50676) were seeded into a black clear-bottom 96-well plate at a density of 1 × 10 4 to 5 × 10 5 cells per well using 1 4 Ringer's solution. Cells were allowed to adhere for two hours.…”

“…Using CLC products from representative United States manufacturers, we then examined the Acanthamoeba strain ATCC 50370 (Figure 4), ATCC 30461 (Figure 5) (as the two most commonly used strains in CLC product testing), and ATCC 50676 (Figure 6) (a more novel strain) using the Process 1 method [8,16]. Images were taken of the fluorescence of each well (subpanel A), and quantifications of each 96-well plate were calculated using a BioTek plate reader (subpanel B).…”

“…Additionally, CLC solutions sold in the European market were investigated against the Acanthamoeba strains ATCC 50370 (Figure 7) and ATCC 30461 (Figure 8) using the Process 1 method, as they are the two most widely tested strains in CLC product research [8,16]. In both strains, OPTI-FREE Puremoist MPDS, OPTI-FREE Express MPDS, and OPTI-FREE Replenish MPDS demonstrated significantly higher FIU (p < 0.001) than Acumed, Lite, renu Multiplus, Avizor, or Visiomax.…”

“…Currently, the United States Food and Drug Administration and other international regulatory bodies require contact lens care solution manufacturers to conduct microbiological testing of CLC solution disinfection against fungi (Fusarium keratoplasticum), yeast (Candida albicans), and bacteria (Pseudomonas aeruginosa, Serratia marcescens, and Staphylococcus aureus) during product registration due to these organisms often being associated with potential ocular infections [7]. Unfortunately, these requirements still do not include Acanthamoeba; however, efforts are underway to make this critical microorganism part of the product registration requirements [8]. Thus, testing for Acanthamoeba is not uniformly addressed among CLC solution manufacturers, and current methods can be considered inefficient and time-consuming.…”

BCLA CLEAR - Contact lens wettability, cleaning, disinfection and interactions with tears

“…Furthermore, there are currently no requirements for manufacturers to test against Acanthamoeba, albeit such testing is often conducted on a voluntary basis [277,278] and there is an ISO standard to test whether MPDS causes Acanthamoeba encystment (ISO 19045:2015(en) Ophthalmic optics -Contact lens care products -Method for evaluating Acanthamoeba encystment by contact lens care products) [279]. While there is interest in incorporating the testing of care solutions against Acanthamoeba for regulatory purposes, there are important issues that need to be solved, such as standardisation of the testing procedure [276,[280][281][282]. Although some care solutions might be effective against Acanthamoeba trophozoites, many are not against the dormant highly resistant cyst stage [277,278,[283][284][285][286][287][288].…”