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.