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Antimicrobial Agents and Chemotherapy, April 2001, p. 1174-1183, Vol. 45, No. 4
0066-4804/01/$04.00+0   DOI: 10.1128/AAC.45.4.1174-1183.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Role of ATP-Binding-Cassette Transporter Genes in High-Frequency Acquisition of Resistance to Azole Antifungals in Candida glabrata

Dominique Sanglard,* Francoise Ischer, and Jacques Bille

Institut de Microbiologie, Centre Hospitalier Universitaire Vaudois, 1011 Lausanne, Switzerland

Received 16 August 2000/Returned for modification 5 January 2001/Accepted 25 January 2001

Candida glabrata has been often isolated from AIDS patients with oropharyngeal candidiasis treated with azole antifungal agents, especially fluconazole. We recently showed that the ATP-binding-cassette (ABC) transporter gene CgCDR1 was upregulated in C. glabrata clinical isolates resistant to azole antifungal agents (D. Sanglard, F. Ischer, D. Calabrese, P. A. Majcherczyk, and J. Bille, Antimicrob. Agents Chemother. 43:2753-2765, 1999). Deletion of CgCDR1 in C. glabrata rendered the null mutant hypersusceptible to azole derivatives and showed the importance of this gene in mediating azole resistance. We observed that wild-type C. glabrata exposed to fluconazole in a medium containing the drug at 50 µg/ml developed resistance to this agent and other azoles at a surprisingly high frequency (2 × 10-4 to 4 × 10-4). We show here that this high-frequency azole resistance (HFAR) acquired in vitro was due, at least in part, to the upregulation of CgCDR1. The CgCDR1 deletion mutant DSY1041 could still develop HFAR but in a medium containing fluconazole at 5 µg/ml. In the HFAR strain derived from DSY1041, a distinct ABC transporter gene similar to CgCDR1, called CgCDR2, was upregulated. This gene was slightly expressed in clinical isolates but was upregulated in strains with the HFAR phenotype. Deletion of both CgCDR1 and CgCDR2 suppressed the development of HFAR in a medium containing fluconazole at 5 µg/ml, showing that both genes are important mediators of resistance to azole derivatives in C. glabrata. We also show here that the HFAR phenomenon was linked to the loss of mitochondria in C. glabrata. Mitochondrial loss could be obtained by treatment with ethidium bromide and resulted in acquisition of resistance to azole derivatives without previous exposure to these agents. Azole resistance obtained in vitro by HFAR or by agents stimulating mitochondrial loss was at least linked to the upregulation of both CgCDR1 and CgCDR2.

* Corresponding author. Mailing address: Institute of Microbiology, University Hospital Lausanne, (CHUV), Rue de Bugnon 44, CH-1011 Lausanne, Switzerland. Phone: 0041 21 3144083. Fax: 0041 21 3144060. E-mail: Dominique.Sanglard{at}chuv.hospvd.ch.

Antimicrobial Agents and Chemotherapy, April 2001, p. 1174-1183, Vol. 45, No. 4
0066-4804/01/$04.00+0   DOI: 10.1128/AAC.45.4.1174-1183.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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