Synergistic mechanisms of retigeric acid B and azoles against Candida albicans

Aims: To clarify the underlying synergistic antifungal mechanisms of retigeric acid B (RAB) in combination with azoles against Candida albicans. Methods and Results: Increased accumulation of rhodamine 123 in C. albicans was measured by both spectrophotometric method and flow cytometry. The inhibitory properties to the drug efflux of C. albicans were determined spectrophotometrically. The decreased cellular ergosterol synthesis was measured using its unique spectrophotometric absorbance profile, and the downregulation expression levels of CDR1 and ERG11 were detected by real-time reverse transcription polymerase chain reaction. Transmission electron microscopy investigation found the wrinkled cell membrane and the impaired cell wall. Conclusions: RAB synergizes the antifungal effect of azoles against C. albicans by inhibiting efflux pump activity, targeting the ergosterol biosynthesis pathway and increasing the fluidity for the resulted ergosterol depletion. Significance and Impact of the Study: Investigating the mechanism of the synergy between RAB and azoles against C. albicans will help us to uncover the antifungal roles of this lichen-derived triterpene acid and find its possible clinical applications in overcoming fungal resistance.