NEW EVIDENCE THAT CANDIDA-ALBICANS POSSESSES ADDITIONAL ATP-BINDING CASSETTE MDR-LIKE GENES - IMPLICATIONS FOR ANTIFUNGAL AZOLE RESISTANCE

Emergence of resistance of Candida albicans to antifungal triazoles is increasingly recognized as an important cause of refractory mucosal c andidiasis in HIV-infected patients. Recently, CDR1, which is thought to be analogous to the human MDR-1 P-glycoprotein, has been cloned in C. albicans. It has been proposed that its expression is partially res ponsible for fluconazole resistance in C. albicans. This gene is chara cterized by the presence of an ATP binding cassette (ABC) region and i s distinct from the BENr gene which does not encode such a functional domain. As the molecular basis for fluconazole resistance appears to b e multifactorial, we considered that there may be other ATP binding ca ssette-containing MDR genes that may potentially contribute to antifun gal azole resistance in C. albicans. We therefore sought to identify p otential target sequences that may be derived from candidate genes tha t share homology with the ATP binding cassette region of the human MDR -1 P-glycoprotein. Degenerate oligonucleotide primers based on the kno wn sequence from the ATP binding cassette region of the human MDR-1 P- glycoprotein were used to amplify PCR products within the range of 100 bp in length from C. albicans isolates (3 fluconazole-susceptible and 3 fluconazole-resistant). Sequence analysis of individually subcloned PCR products, derived from the six isolates revealed 34 sequences in total. The results of our study identified 14 clones (with at least on e per isolate) with a high degree of homology to the ATP binding casse tte of the human MDR-1 P-glycoprotein. The BLAST search did not disclo se homology of these new sequences to the C. albicans CDR1 gene, sugge sting that C. albicans may possess more than one MDR-like gene. We con clude that C. albicans may possess one or more additional genes encodi ng ATP binding cassette MDR-like proteins that are distinct from CDR1 and which could participate in the development of fluconazole resistan ce.