Susceptibility of clinical isolates of Candida species to fluconazole and detection of Candida albicans ERG11 mutations

Objectives: To investigate fluconazole susceptibility of Candida albicans from non-AIDS patients and to analyse the relationship between mutations in the ERG11 gene of these isolates and fluconazole resistance. Methods: Four hundred and twenty-six clinical isolates of Candida species were collected. Fluconazole susceptibility was tested in vitro using microdilution and disc diffusion assays. The ERG11 genes of 23 isolates of C. albicans (8 susceptible and 15 resistant) and 6 type strains (4 susceptible and 2 resistant) were amplified in three overlapping regions of the gene and sequenced. Results: Of the 426 isolates collected, 68.6% were C. albicans; however, only 5.1% were resistant to fluconazole. Eighteen silent mutations and 19 missense mutations were detected. There were six missense mutations only in resistant isolates or resistant type strains: (i) G487T (A114S) and T916C (Y257H) appeared simultaneously in 14 fluconazole-resistant isolates without any other mutation; these may be associated with resistance; (ii) T541C (Y132H) and T1559C (I471T) are known to contribute to fluconazole resistance; and (iii) C1567A (Q474K) or a novel mutation T1493A (F449Y) was identified but correlations with resistance have not been studied. Conclusions: In this survey, C. albicans is the major cause of candidiasis in non-AIDS patients, and some isolates that are resistant to fluconazole have G487T and T916C mutations in ERG11 that are associated with fluconazole resistance.