Evaluation of the conjunctival fungal flora and its susceptibility to antifungal agents in healthy horses in Switzerland

Objective To characterize the conjunctival fungal flora and to determine the susceptibility of 2 isolated molds to antifungal drugs in samples of 64 healthy horses from The National Stud in Switzerland. Procedure Conjunctival cytobrush samples were collected from both eyes of 64 ophthalmologically normal horses in August 2012 and subsequently cultured on Sabouraud's agar medium. Growing fungi were identified and counted. Etests or broth microdilution tests for Aspergillus fumigatus and Eurotium amstelodami were carried out to determine antifungal drug sensitivity. These species had previously been detected in samples from eyes with keratomycosis in Switzerland. Minimal inhibitory concentrations (MICs) for voriconazole, fluconazole, itraconazole, amphotericin B, and miconazole were recorded. Results Fifty-nine of the horses were tested positive for fungal growth from at least one eye (92%). Eleven genera of fungi were identified. The most common fungal genera were Alternaria, Eurotium, Rhizopus, and Cladosporium. Aspergillus spp. and Penicillium spp. were isolated frequently, while no Fusarium spp. was found. In only 2 cases, yeasts were identified as Candida guilliermondii. For certain fungal species, the type of bedding and housing appeared to influence their prevalence. Susceptibility testing of A. fumigatus showed lowest MICs for voriconazole, E. amstelodami for voriconazole and itraconazole. High MICs for fluconazole were detected for all tested fungi while MICs for amphotericin B and miconazole were variable. Conclusions A large range of fungal mold species was identified including A. fumigatus and E. amstelodami, which have been causative agents of keratomycosis in Switzerland. Best in vitro susceptibility results for these two species were obtained for voriconazole.