Efficacy of hand held, inexpensive UV light sources on Acanthamoeba, causative organism in amoebic keratitis

Ivan Cometa¹, Andrew Rogerson¹, Scott Schatz²

¹Department of Biology, California State University Fresno, Fresno, CA, USA; ²Arizona College of Optometry, Midwestern University, Glendale, AZ, USA

Abstract: Multipurpose lens cleaning solutions (MPS) fail to consistently kill or inactivate Acanthamoeba cysts and UV irradiation, while effective at high doses, can damage contact lenses. The present study considered synergy of action between MPS and hand-held inexpensive (ie, relatively weak) UV irradiation units. Regardless of disinfection method recently formed cysts (<10 days) were far more susceptible to treatment than mature cysts (>14 days). This has important implications for future protocols on testing methods for killing amoebae. The study also showed that cysts of different strains (two tested, FLA2 and P120) are variable in their response to MPS, presumably reflecting differences in cyst wall structure and thus permeability to the disinfectant. On the other hand, the effect of UV irradiation was not wall structure dependent. A 6-hour treatment with MPS alone killed trophic amoebae but failed to kill any mature cysts. Cysts of strain FLA2 were killed after 24 hours with MPS but cysts of strain P120 survived. UV irradiation with the larger 4 W unit killed all cysts after 7 minutes and was more effective than the smaller battery-powered unit (after 10 minutes about 50% of cysts were killed). When the larger unit was used with the MPS disinfection, all trophozoites were killed using UV for 3 minutes and MPS for 1 hour. The resistant P120 cysts remained a challenge but a 2- to 4-minute UV treatment followed by MPS for 3 or 6 hours reduced mature cyst survival by about 50%. The small unit in combination with MPS was less effective but did reduce the time required to kill trophic amoebae in MPS (6 hours MPS alone versus 3 hours MPS with a 1-minute UV treatment). In short, inexpensive UV units do enhance MPS disinfection and future lens cleaning systems/protocols might capitalize on this synergistic action.

Keywords: UV light sources, amoebic keratitis, MPS