A Novel Erg3 T208Is Substitution Associated with Reduced Fluconazole and Voriconazole Susceptibility in Clinical Talaromyces marneffei Isolates from HIV/AIDS Patients

Abstract

Introduction Talaromyces marneffei (T. marneffei) is a life-threatening dimorphic fungus endemic to southern China and Southeast Asia. Decreased triazole susceptibility in T. marneffei has emerged as a major clinical challenge for treating immunocompromised patients, particularly those living with HIV/AIDS. This study aimed to explore the mechanisms underlying reduced susceptibility to fluconazole and voriconazole in T. marneffei isolates derived from HIV/AIDS patients in China. Methods Antifungal susceptibility testing of clinical isolates was performed using the broth microdilution method in accordance with CLSI M27-A4 guidelines. Whole-genome sequencing (WGS) and Sanger sequencing were applied to screen for putative resistance-associated genetic mutations, with a focus on the key ergosterol biosynthesis genes Erg3 and cyp51B. Furthermore, sequence conservation analysis was conducted to evaluate the conservation of candidate mutation sites across pathogenic fungi. Results All four clinical isolates exhibited a putative resistance phenotype to fluconazole and voriconazole, with significantly higher minimum inhibitory concentrations (MICs) compared with the wild-type strain. A novel Erg3 c.1195G>A (p.T208I) substitution was identified in three isolates via genomic sequencing. Bioinformatic analysis verified that the T208 residue is highly conserved among T. marneffei and other pathogenic fungi. Conclusion This is the first study to identify an association between the Erg3 T208I substitution and putative cross-resistance to fluconazole and voriconazole in T. marneffei. The findings of expand the known genetic mechanisms underlying putative antifungal resistance in T. marneffei.