Preanalytical conditions for broth microdilution antifungal susceptibility of Microsporum spp.

Dermatophytoses caused by the genus Microsporum require a long-duration therapy compared to infections caused by other genera. Treatment of these cutaneous infections includes topical and systemic antifungal agents. Tinea capitis and tinea unguium caused by M. canis and M. gypseum are the most difficult-to-treat dermatophytoses. There are few specific studies about corresponding antifungal susceptibility in vitro. Recently, the Clinical and Laboratory Standards Institute proposed the M38A document as standard to determine the minimum inhibitory concentrations (MICs) of several antifungal agents against conidium-forming filamentous fungi; however, dermatophytes were not included in this document. This study aimed to contribute to continuing investigations concerning the optimal antifungal susceptibility testing conditions of Microsporum spp. to terbinafine, ciclopiroxolamine and griseofulvin. The results pointed out potato dextrose agar as the best culture medium for inducing conidia sporulation, inoculum density amounting to 1 x 10(3) conidia ml(-1), containing only microconidia, with an incubation time of 7 days at 28 degrees C and 100% growth inhibition serving as an endpoint. The minimum fungicidal concentration values were in accordance with the MICs values, showing a fungicidal activity of these drugs towards the tested strains. According to our results, in general, terbinafine was more active than griseofulvin and ciclopiroxolamine.