Pyrogallol and Fluconazole Interact Synergistically against Candida glabrata through an Efflux-Associated Mechanism.

Candida glabrata is currently the first or second most commonly encountered non- species worldwide. The potential severity of resistance mandates the discovery of novel antifungal agents, including those that can be used in combination therapies. In this study, we evaluated the interactions of pyrogallol (PG) and azole drugs against 22 clinical C. glabrata isolates. The potential mechanism underlying the synergism between PG and fluconazole (FLC) was investigated by the rhodamine 6G efflux method and quantitative reverse transcription (qRT)-PCR analysis. In susceptibility tests, PG showed strong synergism with FLC, itraconazole (ITC), and voriconazole (VRC), with fractional inhibitory concentration index values of 0.18 to 0.375 for PG+FLC, 0.250 to 0.750 for PG+ITC, and 0.141 to 0.750 for PG+VRC. Cells grown in the presence of PG+FLC exhibited reduced rhodamine 6G extrusion and significantly downregulated expression of the efflux-related genes , , and compared with cells grown in the presence of PG or FLC alone. PG did not potentiate FLC when tested against a Δ strain. Restoration of a functional allele also restored the synergism. These results indicate that PG is an antifungal agent that synergistically potentiates the activity of azoles. Furthermore, PG appears to exert its effects by inhibiting efflux pumps and downregulating , , and , with probably playing a crucial role in this process.