Efflux-mediated multidrug resistance mechanism in Trichophyton indotineae and Trichophyton rubrum; role of ABC transporters and MFS gene

Abstract Background An unprecedented surge in chronic, recalcitrant, and resistant dermatophytosis has been observed, predominantly caused by Trichophyton indotineae. While terbinafine resistance is usually linked to squalene epoxide gene (SE) mutations, azole-resistance involves CYP51B overexpression and target gene mutations. Objective To investigate the role of multidrug efflux-transporters and Erg1 in terbinafine and fluconazole-resistant T. indotineae. The secondary aim was to examine a similar mechanism in T. rubrum. Methods Quantitative real-time PCR assessed ABC-transporters, major facilitator superfamily (MFS)-transporters, and Erg1 expression in 63 Trichophyton spp. isolates to explore antifungal resistance mechanisms. For the terbinafine exposure experiment, 39 isolates were tested, while 26 isolates were used for the fluconazole exposure experiment, giving a combined total of 65. Additionally, mutation analysis of the SE and Erg11A genes was performed. Results In T. indotineae, terbinafine exposure induced significant expression of MDR1 and MDR2 in terbinafine-resistance wild-type (TiTR-WT; P < 0.0001), with lower gene-expression for MDR1 and MDR2 noted in terbinafine-resistance with F397L-mutation (TiTR-M) and terbinafine-sensitive wild type. MFS1 gene-expression was significantly higher in TiTR-WT (P < 0.001). In T. rubrum, significant MDR1 induction was found in TrTR-WT isolates (3.88-fold; P < 0.0462). Fluconazole exposure showed significant MDR1, MDR2 and MDR3 expression in T. indotineae resistant isolates. Similarly, fluconazole-resistant T. rubrum isolates showed higher expression of MDR1, MDR2, MDR3, MDR5, MFS1 and SE genes. Conclusions Our study provides valuable insights into the expression patterns of efflux-pump genes in Trichophyton spp. and their role in antifungal resistance. TiTR-WT predominantly upregulate MDR1, MDR2, MFS1, while SE-mutant strains compensate via SE gene overexpression in T. indotineae.