Exploring microwave irradiation as a method to disinfect contact lens cases.

Abstract

PURPOSE\nBiofilm formation caused by infrequent contact lens case replacement and the ineffectiveness of multi-purpose solutions (MPS) on biofilm removal is associated with high rates of bacterial keratitis infections. This study demonstrated biofilm elimination from the contact lens case by microwave irradiation.\n\n\nMETHODS\nStaphylococcus aureus biofilms indicative of 3-9\xa0months of contact wear were cultured in contact lens cases and visualized with crystal violet (CV) staining. Biofilms in contact cases were then exposed to four treatment regimens: No treatment (n\xa0=\xa08), 45\xa0s microwave irradiation (n\xa0=\xa08), tap water (n\xa0=\xa06), and MPS (n\xa0=\xa09). Bacterial survival was assessed by colony forming unit (CFU) assay using streak dilutions.\n\n\nRESULTS\nVisualization of the biofilms through CV staining revealed that biofilms coalesce between ribs of the contact case. In 5/8 cases no CFU were cultivated from the case after treatment with microwave irradiation. In tap water and MPS the first dilution averaged 6\xa0±\xa02 and 31\xa0±\xa013 CFUs per plate, respectively, while microwave irradiation averaged\xa0<\xa01\xa0CFU per plate. In Dilution 2, the average reduced to 0.7\xa0±\xa00.7 and 6\xa0±\xa05 CFUs per plate for tap water and MPS, respectively, while microwave irradiation had 0 CFUs in Dilution 2.\n\n\nCONCLUSION\nBiofilms that coalesce between the ribs of the contact case pose a threat because this area is difficult to thoroughly scrub and could act as a basis for infection through fouling of contact lenses. Of the four treatment regimens, microwave irradiation displayed the most consistent and highest rate of bacterial eradication. Tap water was less effective compared to microwave irradiation, and poses other harmful side effects, but greatly reduced CFU count compared to no treatment. MPS displayed the poorest bacterial eradication of the treatments. Thus, microwave irradiation is worth further investigation as a viable in-home disinfecting option.