Clinical Talaromyces marneffei isolates exhibit enhanced stress tolerance and diminished antifungal responsiveness relative to non-clinical strains.

Abstract

Introduction: Talaromycosis, caused by the dimorphic fungus Talaromyces marneffei, is a significant opportunistic infection in HIV/AIDS patients in Southeast Asia. This study aimed to investigate the antifungal susceptibility of clinical T. marneffei strains (from HIV-positive and HIV-negative patients) and non-clinical strains, and to compare their adaptability to various stress conditions.

Methods: A total of 196 T. marneffei strains were assessed using broth microdilution and Sensititre YeastOne YO10 methods to determine MICs against nine antifungal agents. Stress adaptability was evaluated using 20 randomly selected non-clinical and 20 clinical strains incubated under KCl, Congo red (CR), H₂O₂, and Calcofluor white (CFW).

Results: Azole antifungals (itraconazole, voriconazole, posaconazole) exhibited low MICs, indicating strong activity; Clinical strains showed higher geometric mean MICs for most antifungals than non-clinical strains. Non-clinical strains showed significantly less adaptability to stress than clinical strains under CR, H₂O₂, and CFW (p<0.05), with smaller colony diameters and slower growth.

Discussion: These findings suggest that non-clinical strains may undergo phenotypic adaptations when infecting human hosts, enhancing their resilience to environmental factors and immune pressures. Antifungal susceptibility was not associated with HIV status or patient age, but linked to host adaptation.