Screening of Transcriptomic Factors Associated with Multidrug-Resistant Candida krusei

Abstract

Oral candidiasis is a common fungal infection caused by Candida species, often exhibiting resistance to antifungal agents. Among non-albicans Candida species, Candida krusei is of clinical concern due to the development of resistance mechanisms, including drug efflux pumps and gene overexpression. This study investigates drug susceptibility, minimum inhibitory concentration (MIC), efflux pump activity, and gene expression in C. krusei isolates. After identification using chromogenic media (HiCrome Candida Differential Agar), clinical isolates were subjected to antifungal susceptibility testing and MIC determination against fluconazole, voriconazole, miconazole, clotrimazole, and nystatin following CLSI guidelines. Efflux pump activity was evaluated using the Rhodamine 6G (R6G) efflux assay. Gene expression of CDR1, CDR2, TAC1, and ERG11- key regulators of azole resistance—was analyzed using RT-qPCR and the 2^−∆∆CT method. The antifungal susceptibility profiling revealed that the majority of the clinical isolates exhibited resistance to nystatin with an MIC of ≥ 8μg/mL, while the MIC ranges 0.25-2μg/mL for other drugs. Notably, higher R6G efflux was observed in nystatin exposure compared to other antifungals, indicating a contributory role of ATP-binding cassette (ABC) transporters to antifungal resistance- especially in reducing intracellular drug accumulation. Further support for this mechanism was provided by RT-qPCR analysis, which showed upregulation of resistance-associated genes- CDR1, CDR2, TAC1, and ERG11- pre-treated with nystatin. The increased efflux activity observed in the R6G assay and overexpression of these efflux genes, especially in response to nystatin, underscores the pivotal role of efflux pumps in mediating resistance. These findings suggest that targeting efflux-mediated pathways may be a promising strategy in overcoming resistance in Candida infections.

J. Bio-Sci. 34(1): 22-30, 2026