Identification and expression of multidrug transporters responsible for fluconazole resistance in Candida dubliniensis.
Candida dubliniensis is a recently described Candida species associated with oral candidosis in human immunodeficiency virus (HIV)-infected and AIDS patients, from whom fluconazole-resistant clinical isolates have been previously recovered. Furthermore, derivatives exhibiting a stable fluconazole-resistant phenotype have been readily generated in vitro from fluconazole-susceptible isolates following exposure to the drug. In this study, fluconazole-resistant isolates accumulated up to 80% less [3H] fluconazole than susceptible isolates and also exhibited reduced susceptibility to the metabolic inhibitors 4-nitroquinoline-N-oxide and methotrexate. These findings suggested that C. dubliniensis may encode multidrug transporters similar to those encoded by the C. albicans MDR1, CDR1, and CDR2 genes (CaMDR1, CaCDR1, and CaCDR2, respectively). A C. dubliniensis homolog of CaMDR1, termed CdMDR1, was cloned; its nucleotide sequence was found to be 92% identical to the corresponding CaMDR1 sequence, while the predicted CdMDR1 protein was found to be 96% identical to the corresponding CaMDR1 protein. By PCR, C. dubliniensis was also found to encode homologs of CDR1 and CDR2, termed CdCDR1 and CdCDR2, respectively. Expression of CdMDR1 in a fluconazole-susceptible delta pdr5 null mutant of Saccharomyces cerevisiae conferred a fluconazole-resistant phenotype and resulted in a 75% decrease in accumulation of [3H]fluconazole. Northern analysis of fluconazole-susceptible and -resistant isolates of C. dubliniensis revealed that fluconazole resistance was associated with increased expression of CdMDR1 mRNA. In contrast, most studies showed that overexpression of CaCDR1 was associated with fluconazole resistance in C. albicans. Increased levels of the CdMdr1p protein were also detected in fluconazole-resistant isolates. Similar results were obtained with fluconazole-resistant derivatives of C. dubliniensis generated in vitro, some of which also exhibited increased levels of CdCDR1 mRNA and CdCdr1p protein. These results demonstrate that C. dubliniensis encodes multidrug transporters which mediate fluconazole resistance in clinical isolates and which can be rapidly mobilized, at least in vitro, on exposure to fluconazole.
Moran
G P
GP
Department of Oral Surgery, Oral Medicine and Pathology, School of Dental Science, Trinity College, University of Dublin, Republic of Ireland.
Sanglard
D
D
Donnelly
S M
SM
Shanley
D B
DB
Sullivan
D J
DJ
Coleman
D C
DC
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics* / Q000378:metabolism; D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism; D000595:Amino Acid Sequence; D000935:Antifungal Agents / Q000378:metabolism / Q000494:pharmacology*; D001483:Base Sequence; D002175:Candida / Q000187:drug effects* / Q000235:genetics*; D002176:Candida albicans / Q000235:genetics; D004352:Drug Resistance, Microbial / Q000235:genetics; D018432:Drug Resistance, Multiple / Q000235:genetics*; D015725:Fluconazole / Q000378:metabolism / Q000494:pharmacology*; D005656:Fungal Proteins / Q000235:genetics; D015966:Gene Expression Regulation, Fungal; D006801:Humans; D026901:Membrane Transport Proteins; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D012441:Saccharomyces cerevisiae; D017386:Sequence Homology, Amino Acid
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D018528:ATP-Binding Cassette Transporters; D000935:Antifungal Agents; C094693:CDR1 protein, Candida albicans; D005656:Fungal Proteins; D026901:Membrane Transport Proteins; D015725:Fluconazole