Terbinafine Resistance of Trichophyton Clinical Isolates Caused by Specific Point Mutations in the Squalene Epoxidase Gene.

Terbinafine is one of the allylamine antifungal agents whose target is squalene epoxidase (SQLE). This agent has been extensively used in the therapy of dermatophyte infections. The incidence of patients with tinea pedis or unguium tolerant to terbinafine treatment prompted us to screen the terbinafine resistance of all javax.xml.bind.JAXBElement@dc06fb4 clinical isolates from the laboratory of the Centre Hospitalier Universitaire Vaudois collected over a 3-year period and to identify their mechanism of resistance. Among 2,056 tested isolates, 17 (≈1%) showed reduced terbinafine susceptibility, and all of these were found to harbor javax.xml.bind.JAXBElement@374d721c gene alleles with different single point mutations, leading to single amino acid substitutions at one of four positions (Leu javax.xml.bind.JAXBElement@4655f570 , Phe javax.xml.bind.JAXBElement@112b804a , Phe javax.xml.bind.JAXBElement@1f18e014 , and His javax.xml.bind.JAXBElement@4319ac79 ) of the SQLE protein. Point mutations leading to the corresponding amino acid substitutions were introduced into the endogenous javax.xml.bind.JAXBElement@2a0e3f1f gene of a terbinafine-sensitive javax.xml.bind.JAXBElement@67eac3c4 (formerly javax.xml.bind.JAXBElement@3f2a876d ) strain. All of the generated javax.xml.bind.JAXBElement@315e9e95 transformants expressing mutated SQLE proteins exhibited obvious terbinafine-resistant phenotypes compared to the phenotypes of the parent strain and of transformants expressing wild-type SQLE proteins. Nearly identical phenotypes were also observed in javax.xml.bind.JAXBElement@6af3a966 transformants expressing mutant forms of javax.xml.bind.JAXBElement@5bb6b31f SQLE proteins. Considering that the genome size of dermatophytes is about 22 Mb, the frequency of terbinafine-resistant clinical isolates was strikingly high. Increased exposure to antifungal drugs could favor the generation of resistant strains

Gene Amplification of CYP51B: a New Mechanism of Resistance to Azole Compounds in Trichophyton indotineae.

Trichophyton indotineae causes dermatophytosis that is resistant to terbinafine and azole compounds. The aim of this study was to determine the mechanisms of resistance to itraconazole (ITC) and voriconazole (VRC) in strains of T. indotineae. Two azole-sensitive strains (ITC MIC < 0.125 μg/mL; VRC MIC < 0.06 μg/mL) and four azole-resistant strains (ITC MIC ≥ 0.5 μg/mL; VRC MIC ≥ 0.5 μg/mL) were used for the investigation. The expression of MDR genes encoding multidrug transporters of the ABC family for which orthologs have been identified in Trichophyton rubrum and those of CYP51A and CYP51B encoding the targets of azole antifungal compounds were compared between susceptible and resistant strains. TinMDR3 and TinCYP51B were overexpressed in T. indotineae resistant strains. Only small differences in susceptibility were observed between TinMDR3 disruptants and parental strains overexpressing TinMDR3. Whole-genome sequencing of resistant strains revealed the creation of a variable number of TinCYP51B tandem repeats at the specific position of their genomes in three resistant strains. Downregulation of TinCYP51B by RNA interference (RNAi) restored the susceptibility of azole-resistant strains. In contrast, overexpression of TinCYP51B cDNA conferred resistance to a susceptible strain of T. indotineae. In conclusion, the reduced sensitivity of T. indotineae strains to azoles is mainly due to the overexpression of TinCYP51B resulting from additional copies of this gene

DNA topoisomerase 2 gene polymorphism in dermatophytes

Background: Dermatophytes are a group of keratinophilic fungi of medical importance. Despite a relatively long history of molecular taxonomic studies, there is still a need for information on genetic polymorphism in wider variety of genomic loci. Objectives: Our goal was to study partial DNA topoisomerase 2 gene (TOP2) polymorphism in dermatophytes. Methods: We performed DNA sequencing of TOP2 in 26 dermatophyte species along with ribosomal internal transcribed spacer (ITS) sequencing. Results: The number of polymorphic sites in TOP2 data set was similar to that one in ITS data set. Nannizzia species formed paraphyletic group in TOP2 tree. Trichophyton simii was paraphyletic in concatenated TOP2-ITS tree, one of its two clades contained solely Iranian isolates. Conclusions: Our results revealed several unresolved problems in the taxonomy of dermatophytes, including probable polyphyly of the genus Nannizzia and the species T simii