Antifungal activities of tacrolimus and azole agents against the eleven currently accepted Malassezia species

Abstract

The lipophilic yeast Malassezia is an exacerbating factor in atopic dermatitis (AD) and colonizes the skin surface of patients with AD. With the goal of reducing the number of Malassezia cells, we investigated the antifungal activities of a therapeutic agent for AD, tacrolimus, and the azole agents itraconazole and ketoconazole against Malassezia species in vitro. We examined 125 strains of the 11 currently accepted Malassezia species by using the agar dilution method. All strains of the 11 Malassezia species were very susceptible to both azole agents, with MICs ranging from 0.016 to 0.25 mug/ml. Tacrolimus had antifungal activities against half of the strains, with MICs ranging from 16 to 32 mug/ml. Two of the major cutaneous floras, Malassezia globosa and Malassezia restricta, have several genotypes in the intergenic spacer region of the rRNA gene; the azole agents had slightly higher MICs for specific genotype strains of both microorganisms. A combination of azole agents and tacrolimus had a synergistic effect against Malassezia isolates, based on a fractional inhibitory index of 0.245 to 0.378. Our results provide the basis for testing these agents in future clinical trials to reduce the number of Malassezia cells colonizing the skin surface in patients with AD.

FIG. 1.

Molecular phylogenetic tree of the M. globosa isolates. A tree was constructed from IGS1 sequences of the rRNA gene by using a neighbor-joining analysis (21) after the sequences were aligned by using ClustalW (31). The distances between sequences were calculated by using Kimura's two-parameter model (12). The numbers indicate the confidence levels from 100 replicate bootstrap samplings (frequencies less than 50% are not shown) (6). HS, healthy subject. Knuc, Kimura’s parameter (12).

FIG. 2.

Molecular phylogenetic tree of M. restricta isolates. The tree was constructed using the method described in the legend for Fig. 1. HS, healthy subject. Knuc, Kimura’s parameter (12).