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

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 .