MULTIPLE EFFLUX MECHANISMS ARE INVOLVED IN CANDIDA-ALBICANS FLUCONAZOLE RESISTANCE

Fluconazole-susceptible Candida albicans strains accumulated [H-3]fluc onazole at a rate of approximately 2 pmol/min per 10(9) cells. Flucona zole accumulation was not affected by the pretreatment of cells with s odium azide or with 2-deoxyglucose. The rate of fluconazole accumulati on became saturated at high fluconazole concentrations and was not aff ected by the addition of ketoconazole, and there was no fluconazole ac cumulation in cells incubated at 4 degrees C. A fluconazole-resistant mutant of C. albicans SGY-243 was isolated following growth enrichment in fluconazole-containing medium. Cells of the mutant strain, designa ted FR2, showed a reduced rate of fluconazole accumulation compared wi th SGY-243 and were not resistant to other azole antifungal agents. Th e rates of fluconazole accumulation by C. albicans FR2 and the other a zole-resistant strains, B59630, AD, and KB, were increased in the pres ence of sodium azide, suggesting that fluconazole resistance in these strains may be associated with an energy-dependent drug efflux. Flucon azole-resistant C. albicans strains all contained elevated amounts (2- to 17-fold) of mRNA encoding Cdr1, an ATP-binding cassette-type trans porter. In addition, C. albicans FR2 also contained increased amounts of mRNA encoding Ben(r), a major facilitator superfamily transporter. These results suggest that fluconazole enters C. albicans cells by fac ilitated diffusion and that fluconazole resistance may involve energy- dependent drug efflux associated with increased expression of Ben(r) a nd/or Cdr1.