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Updated: Jun 17, 2026
Quantification of Acanthamoeba spp. Motility
Published on: September 20, 2024
Disinfection efficacy and encystment rate of soft contact lens multipurpose solutions against Acanthamoeba
James Lonnen1, Wayne Heaselgrave, Miya Nomachi
1Department of Infection, Immunity and Inflammation, University of Leicester, Medical Sciences Building, Leicester, United Kingdom.
Objectives:
To assess the ability of commercial and experimental soft contact lens multipurpose solutions (MPS) to promote Acanthamoeba trophozoite encystment and their biocidal efficacy against Acanthamoeba trophozoites and cysts. The effects on encystment and disinfection efficacy by the incorporation of propylene glycol (PG) in the formulation of MPS were also investigated.
Methods:
Acanthamoeba trophozoites (Acanthamoeba castellanii ATCC 50730 and Acanthamoeba polyphaga CCAP 1501/3G) were inoculated into MeniCare Soft, MeniCare Soft (-PG), Epica Cold II, OptiFree Plus, and Rohto C cube Softone-Moist MPS, and the percentage of encystment induced by each solution was determined after 24 hr. In addition, Acanthamoeba trophozoites and cysts (A. castellanii ATCC 50730 and A. polyphaga CCAP 1501/3G and Ros) were also inoculated into each of the five MPS, and their log reduction determined after 0, 1, 4, 6, and 24 hr of incubation using stand-alone assays.
Results:
Significantly higher encystment rates were found with Epica Cold II for A. polyphaga CCAP 1501/3G and Rohto C cube Softone-Moist for A. polyphaga and A. castellanii compared with the other MPS assessed (P<0.05). MeniCare Soft, MeniCare Soft (-PG), and Opti-Free Plus produced little or no encystment, with mean encystment values ranging from 0.0% to 2.0%. A significantly higher disinfection efficacy was found with MeniCare Soft, MeniCare Soft (-PG), and Epica Cold II compared with Opti-Free Plus and Rohto C cube Softone-Moist (P<0.05).
Conclusions:
Significant differences in encystment rate and disinfection efficacy between MPS were found. The presence of PG in the formulation of MeniCare Soft did not affect the disinfection efficacy or the encystment rate. The latter indicates that other factors play a role in the induction of Acanthamoeba encystment after inoculation into MPS.
Insights
Multipurpose solutions (MPS) for soft contact lenses show varying efficacy in preventing Acanthamoeba encystment and killing the parasite. Propylene glycol (PG) did not impact MeniCare Soft
Area of Science:
- Ophthalmology
- Microbiology
- Biotechnology
Background:
- Acanthamoeba keratitis is a severe microbial keratitis associated with contact lens wear.
- Multipurpose solutions (MPS) are used for cleaning and disinfecting soft contact lenses.
- The ability of MPS to prevent Acanthamoeba encystment and their biocidal efficacy are critical for ocular health.
Purpose of the Study:
- To evaluate the encystment-inducing and biocidal properties of commercial and experimental soft contact lens MPS against Acanthamoeba.
- To investigate the role of propylene glycol (PG) in MPS formulations on Acanthamoeba encystment and disinfection efficacy.
Main Methods:
- Acanthamoeba trophozoites and cysts were exposed to five different MPS (MeniCare Soft, MeniCare Soft (-PG), Epica Cold II, OptiFree Plus, Rohto C cube Softone-Moist).
- Encystment rates were determined after 24 hours of incubation.
- Biocidal efficacy was assessed by measuring log reduction of trophozoites and cysts at various time points (0, 1, 4, 6, and 24 hours).
Main Results:
- Epica Cold II and Rohto C cube Softone-Moist induced significantly higher Acanthamoeba encystment rates compared to other MPS.
- MeniCare Soft, MeniCare Soft (-PG), and Opti-Free Plus showed minimal to no encystment induction.
- MeniCare Soft, MeniCare Soft (-PG), and Epica Cold II demonstrated significantly higher disinfection efficacy against Acanthamoeba than Opti-Free Plus and Rohto C cube Softone-Moist.
Conclusions:
- Significant variations exist in the encystment promotion and disinfection capabilities of different MPS.
- Propylene glycol (PG) inclusion in MeniCare Soft did not influence its disinfection efficacy or Acanthamoeba encystment rate.
- Factors beyond PG content play a crucial role in inducing Acanthamoeba encystment when exposed to MPS.
