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

Abstract

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 (128 eyes) from the national stud in Switzerland.
Procedure: Conjunctival cytobrush samples were collected from both eyes of 64 ophthalmologically normal horses and subsequently cultured on Sabouraud’s agar medium. Growing fungi were identified and counted. E-tests 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 for voriconazole, fluconazole, itraconazole, amphotericin B and miconazole were recorded to evaluate drug sensitivity.
Results: Eleven genera of fungi were identified. The most common fungal genera were Alternaria, Rhizopus, Cladosporium and Eurotium. Aspergillus spp. and Penicillium spp. were isolated frequently, while no Fusarium spp. was found. In only 2 cases yeasts were identified as Candida guillermondii. For certain fungal species bedding and housing (indoor vs. outdoor) appeared to influence their prevalence. Susceptibility testing of A. fumigatus and E. amstelodami showed consistently best results with low MICs for voriconazole. High MICs for fluconazole were detected for all tested fungi while MICs for itraconazole, 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.
Support: ECVO Research Grant 2012