Abstract
Abstract: :
Purpose: While the efficacy of contact lens disinfecting solutions (CLS) is tested against laboratory or clinical isolates, little is known about their ability to inhibit microbial growth when tested against environmental isolates. This study tested the killing effect of five CLS against eleven environmental yeast isolates obtained from beach sand in south Florida. Methods: The tested CLS were Clear Care, COMPLETE Moisture PLUS, OPTI–FREE Express, ReNu MultiPlus and SOLO–care PLUS. Sabouraud's dextrose broth cultures of Candida albicans, C. krusei, C. parapsilosis, C. tropicalis, Metschnikowia bicuspidata, Pichia anomala, P. ohmeri, P. onychis, Rhodotorula mucilaginosa, Torulaspora delbrueckii and Yarrowia lipolytica were incubated at 23 C, while shaking, for 10 days. Cultures were centrifuged at 1400 rpm for 5 min, resuspended in phosphate buffered water (PBW), centrifuged and resuspended in PBW. One ml of each species containing approximately 107 cells/ml was placed into 9.0 ml of each CLS. Samples were removed from each mixture after 1 min, 30 min, 2 hrs and 4 hrs incubation times, diluted with PBW, spread on 3 Sabouraud's dextrose agar plates, incubated at 23 C for 72 hrs and colony forming units (CFU) were counted. Results: All of the CLS eliminated 99% of the yeasts within 2 hrs. Clear Care, Opti–Free and Renu eliminated 100% of the organisms within 4 hours. The differences between the killing of the isolates by the CLS treatments were significantly different (p<.05, students t–test) at one min exposure time when compared to 0.5, 2 or 4 hrs post–treatment. Differences were not observed after one min. C. parapsilosis was most resistant to the five CLS following initial one min exposure but resistance was overcome after 30 min treatment. Complete was the least effective CLS with six of the yeast isolates displaying an increase in numbers above the original inoculum after one minute of exposure. Conclusions: Environmental yeast isolates proved to be as susceptible as standard challenge organisms to commercially available CLS. The initial resistance of C. parapsilosis may be attributed to the formation of pseudohyphae by C. parapsilosis before treatment thus prolonging the ability of the yeast to resist the effect of the CLS. The increase in the initial inoculum after treatment by Complete may be due to the removal of budding yeast cells from their mother cells before cell death. These data confirm that the CLS are effective against a broad spectrum of environmental yeast isolates.
Keywords: contact lens • fungal disease • cornea: clinical science