The C2H2 Transcription Factor SltA Contributes to Azole Resistance by Coregulating the Expression of the Drug Target Erg11A and the Drug Efflux Pump Mdr1 in Aspergillus fumigatus.

The emergence of azole-resistant fungal pathogens has posed a great threat to public health worldwide. Although the molecular mechanism of azole resistance has been extensively investigated, the potential regulators of azole resistance remain largely unexplored. In this study, we identified a new function of the fungal specific C2H2 zinc finger transcription factor SltA (involved in the salt tolerance pathway) in the regulation of azole resistance of the human fungal pathogen Aspergillus fumigatus A lack of SltA results in an itraconazole hypersusceptibility phenotype. Transcriptional profiling combined with LacZ reporter analysis and electrophoretic mobility shift assays (EMSA) demonstrated that SltA is involved in its own transcriptional regulation and also regulates the expression of genes related to ergosterol biosynthesis (erg11A, erg13A, and erg24A) and drug efflux pumps (mdr1, mfsC, and abcE) by directly binding to the conserved 5'-AGGCA-3' motif in their promoter regions, and this binding is dependent on the conserved cysteine and histidine within the C2H2 DNA binding domain of SltA. Moreover, overexpression of erg11A or mdr1 rescues sltA deletion defects under itraconazole conditions, suggesting that erg11A and mdr1 are related to sltA-mediated itraconazole resistance. Most importantly, deletion of SltA in laboratory-derived and clinical azole-resistant isolates significantly attenuates drug resistance. Collectively, we have identified a new function of the transcription factor SltA in regulating azole resistance by coordinately mediating the key azole target Erg11A and the drug efflux pump Mdr1, and targeting SltA may provide a potential strategy for intervention of clinical azole-resistant isolates to improve the efficiency of currently approved antifungal drugs.

A New Genotype of Trichophyton quinckeanum with Point Mutations in Erg11A Encoding Sterol 14-α Demethylase Exhibits Increased Itraconazole Resistance.

Trichophyton quinckeanum, the causative agent of mouse favus, has been responsible for several infections of animal owners in recent years and showed an infection peak around 2020 in Jena, Thuringia. The isolated T. quinckeanum strains from Thuringia differ in some positions of the ITS region compared to strains from the IHEM collection as well as to Trichophyton schoenleinii. All T. quinckeanum strains of the new genotype show up to a 100-fold increased itraconazole resistance as measured by microplate laser nephelometry (MLN) assays. Analysis of genes involved in Trichophyton indotineae azole resistance, such as Erg1, which encodes squalene epoxidase, and Erg11B, one of two copies of the sterol 14-α demethylase gene, show a 100% identity between the two T. quinckeanum genotypes. In contrast, Erg11A fragments differ in 15-nucleotide positions between both T. quinckeanum genotypes, resulting in the unique amino acid substitution Ala256Ser in resistant strains. The new T. quinckeanum genotype may have evolved through interspecies mating. Mating type analysis showed a nearly 100% identity of the minus type MAT1-1-1 fragment for all T. quinckeanum isolates. The closely related Trichophyton schoenleinii belongs to the plus mating type and has 100% identical fragments of Erg1 and Erg11B. Erg11A protein sequences of T. schoenleinii and T. quinckeanum showed increased diversity.