Characterization of the multi-drug efflux systems of pathogenic fungi using functional hyperexpression in Saccharomyces cerevisiae.

Systemic fungal infections, caused by a wide variety of fungi, contribute to high mortality in humans with immunocompromised conditions. However, there are few classes of antifungal drugs available, limiting therapeutic options. Azoles are the most commonly used class of antifungals to treat many fungal infections, but resistance to azoles can be induced or, for some fungi, is an inherent property. One of major mechanisms of azole resistance is overexpression of drug efflux pumps in fungal cell membranes, such as the energy-dependent ATP-binding cassette (ABC) transporters. We have developed a protein hyperexpression system to facilitate functional analysis of efflux pumps using a Saccharomyces cerevisiae strain as the host for heterologous expression. The system is well suited for the hyperexpression of individual fungal ABC transporters for structural and functional studies. Furthermore, the recombinant yeast strains expressing heterologous membrane proteins can be used to screen for compounds that overcome fungal drug resistance. Also in this review, the mechanisms of azole resistance in Candida glabrata and C. krusei will be considered in relation to the recent increase in the incidence of Candida infections caused by non-albicans Candida. The development of possible novel antifungal agents will also be discussed.