Multiple efflux mechanisms are involved in Candida albicans fluconazole resistance.
Fluconazole-susceptible Candida albicans strains accumulated [3H]fluconazole at a rate of approximately 2 pmol/min per 10(9) cells. Fluconazole accumulation was not affected by the pretreatment of cells with sodium azide or with 2-deoxyglucose. The rate of fluconazole accumulation became saturated at high fluconazole concentrations and was not affected by the addition of ketoconazole, and there was no fluconazole accumulation 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, designated FR2, showed a reduced rate of fluconazole accumulation compared with SGY-243 and were not resistant to other azole antifungal agents. The rates of fluconazole accumulation by C. albicans FR2 and the other azole-resistant strains, B59630, AD, and KB, were increased in the presence of sodium azide, suggesting that fluconazole resistance in these strains may be associated with an energy-dependent drug efflux. Fluconazole-resistant C. albicans strains all contained elevated amounts (2- to 17-fold) of mRNA encoding Cdr1, and an ATP-binding cassette-type transporter. In addition, C. albicans FR2 also contained increased amounts of mRNA encoding Benr, a major facilitator superfamily transporter. These results suggest that fluconazole enters C. albicans cells by facilitated diffusion and that fluconazole resistance may involve energy-dependent drug efflux associated with increased expression of Benr and/or Cdr1.
Albertson
G D
GD
Department of Oral Biology and Oral Pathology, University of Otago, Dunedin, New Zealand.
Niimi
M
M
Cannon
R D
RD
Jenkinson
H F
HF
D000935:Antifungal Agents / Q000032:analysis / Q000494:pharmacology*; D002176:Candida albicans / Q000187:drug effects / Q000235:genetics* / Q000302:isolation & purification; D004352:Drug Resistance, Microbial / Q000235:genetics; D015725:Fluconazole / Q000032:analysis / Q000494:pharmacology*; D005800:Genes, Fungal / Q000235:genetics; D008826:Microbial Sensitivity Tests; D012331:RNA, Fungal / Q000032:analysis
D000935:Antifungal Agents; D012331:RNA, Fungal; D015725:Fluconazole