[Development of resistance in skin fungi : Molecular mechanisms, antifungal resistance assays, risk factors, and diagnostic regime-challenges for medical treatment].

Abstract

The growing prevalence of resistant dermatophyte isolates, particularly from Trichophyton indotineae (synonym: T. mentagrophytes ITS genotype VIII) but also from T. rubrum may lead to increasing numbers of difficult-to-treat dermatomycoses. Terbinafine resistance in T. indotineae or T. rubrum is caused by point mutations that alter specific positions in the Erg1 gene encoding squalene epoxidase, thereby, preventing effective binding of terbinafine to the enzyme. In T. indotineae, two different forms of genomic amplification of Erg11B that lead to azole resistance have been identified. Like Erg11A, Erg11B encodes a form of sterol-14-α-demethylase, whose enzymatic activity is inhibited by azole binding. In T. indotineae as well as in T. rubrum, point mutations in Erg11B have been identified that result in altered amino acid sequences and prevent binding of specific classes of azoles. Another resistance mechanism involves increased expression of transporter proteins responsible for drug efflux. The combination of these various mechanisms presents a major challenge for diagnostics and requires adaptation of both the diagnostic approach and the subsequent therapeutic strategies.