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Published on: September 20, 2024
Encystment of Acanthamoeba during incubation in multipurpose contact lens disinfectant solutions and experimental
Simon Kilvington1, Wayne Heaselgrave, John M Lally
1Department of Infection, Immunity & Inflammation, University of Leicester, Leicester, United Kingdom. sk46@le.ac.uk
Objectives:
Acanthamoeba keratitis (AK) is most commonly found in contact lens wearers with poor lens care hygiene. Recent reports have indicated an increase in cases of AK in the United States associated with the use of Complete MoisturePlus multipurpose solution. This association may not appear explainable by differences in Acanthamoeba kill rates among multipurpose solutions. In this study the physiologic response of Acanthamoeba trophozoites to incubation in various contact lens solutions was investigated.
Methods:
Acanthamoeba trophozoites were incubated in commercial and experimental solutions and the percentage encystment and viability determined in conjunction with microscopic analysis of cyst formation.
Results:
Among commercial products, MoisturePlus solution induced encystment within 6 to 24 hr of incubation. Only immature cysts formed which failed to mature even after 5 days incubation in the solution although they remained viable. Experimental formulations of MoisturePlus solution, modified by omitting key ingredients, identified propylene glycol as the agent responsible for inducing encystment. However, tests of other commercial solutions containing propylene glycol produced reduced or no encystment.
Conclusions:
The presence of propylene glycol was shown to be the key factor in inducing Acanthamoeba encystment. However, the reduced or absence of encystment in other commercial solutions containing propylene glycol suggests additional factors, such the buffering system, may be involved in the phenomenon. How these observations relate to the solution's role in the reported association with AK is unclear. Nevertheless, it is recommended that all lens care products be tested for propensity to induce Acanthamoeba encystment and formulations containing propylene glycol may warrant special scrutiny.
Insights
Propylene glycol in contact lens solutions can induce Acanthamoeba encystment, a key step in Acanthamoeba keratitis (AK) development. Further research is needed to understand factors influencing this response and ensure contact lens solution safety.
Area of Science:
- Ophthalmology
- Microbiology
- Parasitology
Background:
- Acanthamoeba keratitis (AK) is a severe eye infection often linked to contact lens wear and poor hygiene.
- Recent increases in AK cases in the US have been associated with specific multipurpose contact lens solutions.
- The mechanism behind this association may not be solely due to Acanthamoeba kill rates.
Purpose of the Study:
- To investigate the physiological response of Acanthamoeba trophozoites when incubated in various contact lens solutions.
- To identify specific ingredients in contact lens solutions that may influence Acanthamoeba encystment.
Main Methods:
- Acanthamoeba trophozoites were incubated in commercial and experimental contact lens solutions.
- Encystment rates and viability were determined.
- Microscopic analysis was used to examine cyst formation.
Main Results:
- MoisturePlus solution induced Acanthamoeba encystment within 6-24 hours, forming immature, viable cysts.
- Propylene glycol was identified as the primary agent responsible for inducing encystment in experimental formulations.
- Other commercial solutions containing propylene glycol showed reduced or no encystment, suggesting additional factors are involved.
Conclusions:
- Propylene glycol is a key factor in inducing Acanthamoeba encystment.
- Buffering systems and other factors in contact lens solutions may modulate the encystment response.
- All lens care products should be tested for their propensity to induce Acanthamoeba encystment, with special attention to formulations containing propylene glycol.
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