Efflux Pump Inhibition Assay

Overexpression of drug efflux pumps located at the plasma membrane is considered a mechanism for fungal escape from the action of antifungal drugs (Hans et al., 2019). To evaluate the effect of scopoletin on the efflux pump inhibition we performed a phenotypic susceptibility assay (Hans et al., 2019) using promethazine, an inhibitor of plasma membrane efflux pumps. First, the MIC value of promethazine (12.5 a 0.01 μg/mL) for C. tropicalis was tested by broth microdilution method. Second, a new MIC assay for fluconazole (250 to 3.9 μg/mL) was performed including sub-inhibitory concentrations of promethazine (MIC/4 = 0.78 μg/mL) or scopoletin (MIC/4 = 12.5 μg/mL) to the final fungal inoculum.