Comparative in vitro effectiveness of a novel contact lens multipurpose solution on Acanthamoeba castellanii

BACKGROUND: A multipurpose contact lens cleaning solution (MPS) containing novel active ingredients under development was compared to two commercially available MPS solutions for effectiveness against Acanthamoeba isolates. METHODS: The Acanthamoeba isolate A. castellanii was propagated for trophozoite or cyst-containing cultures for the purpose of assessment of effectiveness of each MPS. An alamar blue-based cellular respiration assay was used to assess effectiveness against trophozoites; Trypan blue hemocytometer-based microscopic counts measured cysticidal effects. To assess the general antimicrobial potency of each solution as controls for the anti-amoebic assays, comparative bactericidal effectiveness using Serratia marcenses was also performed. RESULTS: Minimal effectiveness against either Acanthamoeba form was observed from either commercial MPS. In contrast, the novel MPS achieved complete kill within 1 h contact time for both Acanthamoeba trophozoite and cysts. Each commercial MPS required 6 h contact time to achieve a two to three log reduction in S. marcenses. In contrast, the experimental MPS achieved disinfection in 60 min contact time, and complete kill (< 1 CFU) at 90 min. CONCLUSIONS: Results suggest that the inclusion of a novel ingredient combination within the MPS under development clearly is required and is ideal for rapid and effective killing of Acanthamoeba species in the context of contact lens disinfection systems. The representative commercially available MPS used in this testing provided minimal effectiveness against the protozoa regardless of contact time. In addition, comparative results with the bacterial agent in the control study show distinct differences in the speed to disinfection with the novel MPS. Future MPS development should consider inclusion of novel chemical entities that are effective against Acanthamoeba species to speed disinfection and further reduce the exposure potential of users of contact lenses and cleaning systems.