Molecular analysis of cyp51 from fluconazole-resistant Candida albicans strains.

The target enzyme for fluconazole is sterol 14 alpha-demethylase, a cytochrome P450 encoded by cyp51. One mechanism of fluconazole resistance likely to occur in Candida albicans is through an altered target site. To test this hypothesis DNA sequencing of the cyp51 coding sequence from 19 fluconazole-resistant and 19 fluconazole-sensitive C. albicans was undertaken. A number of point mutations were identified in the resistant isolates which were not present in the sensitive ones: F105L (five), E266D (five), K287R (one), G448G (one), G450E (one), G464S (three) and V488I (one). These alterations are discussed in the light of a molecular model of the enzyme regarding potential roles in resistance. It was also demonstrated that sequence-specific primers can be employed to identify polymorphisms which may be associated with resistance; diagnostic tests for resistant strains will prove of value in combating this serious clinical problem.