Antifungal activity of naftifine against various yeasts and dermatophytes: determination of minimal inhibitory concentrations and revelation of cell wall alterations by scanning electron microscopy

Abstract

The in vitro antifungal activity of naftifine, an allylamine derivative, was compared with that of econazole and clotrimazole, imidazole derivatives. The minimal inhibitory concentration (MIC) values were determined against 136 strains of yeasts (Candida albicans, Candida guilliermondii, Candida krusei, Candida parapsilosis, Candida pseudotropicalis, Candida tropicalis, Torulopsis glabrata, Malassezia furfur) and 45 strains of dermatophytes (Microsporum canis, Microsporum gypseum, Microsporum langeronii, Trichophyton mentagrophytes, Trichophyton rubrum, Epidermophyton floccosum). The fungistatic activity was evaluated by the agar dilution method, using various media: YNB (pH 6) for Candida and Torulopsis, Dixon (pH 5.6) for Malassezia, and Sabouraud (pH 6.8) for dermatophytes. The MIC was evaluated at 28–30 °C after incubation for 24–48 h for Candida and Torulopsis and for 3 days for the dermatophytes. Malassezia were incubated for 3 days at 37 °C. Naftifine was highly active against all the dermatophytes tested and moderately or weakly active against the yeasts. Candida parapsilosis was the most sensitive of all the Candida species tested. The effects of naftifine on C. parapsilosis, Mi. canis, and Tr. mentagrophytes were studied by scanning electron microscopy. Naftifine acted on C. parapsilosis causing formation of convolutions and wrinkles and defective separation between mother and daughter yeast cells. Naftifine caused alterations of the dermatophyte cell wall and particularly the hyphal filaments. These alterations were dose and time dependent. The most prominent changes seen by scanning electron microscopy were swelling, ballooning of the hyphae, and bulbiform blunt hyphae ends. Key words: naftifine, Candida, Torulopsis, Malassezia, dermatophytes.