Modulation of the antifungal activity of new medicinal plant extracts active on Candida glabrata by the major transporters and regulators of the pleiotropic drug-resistance network in Saccharomyces cerevisiae.

The increased incidence of drug-resistant fungal infections, a process in which active efflux plays an important role, calls for the development of new treatments. Candida albicans and Candida glabrata are the most frequent human fungal pathogens. The latter, in spite of its increased azole tolerance, is rarely used in medicinal plant screening. Several extracts inhibiting the growth of this pathogenic yeast are identified here. The ethyl acetate extract of the herb Dalea formosa of the American Southwest, not previously known to possess antifungal activity, proved most active against azole-sensitive and azole-resistant isolates. The model yeast Saccharomyces cerevisiae, related to C. glabrata, was used to evaluate the influence of multidrug efflux on the antifungal activity of identified extracts and selected fractions from further purification steps, together with their ability to modulate ketoconazole resistance. The differential involvement of the major pleiotropic drug transporters of the ATP-binding cassette superfamily Pdr5p, Snq2p, and Yor1p as well as their transcriptional activators Pdr1p and Pdr3p in the detoxification of the antifungal constituents of several important medicinal plants is demonstrated. These include Artemisia annua and its widely used antimalarial component artemisinin. This approach revealed the concomitant presence of multidrug efflux pump substrates and modulators in the extract of A. annua and also allowed the identification of an extract not affected by the major pleiotropic drug-resistance genes.