Prevalence of molecular mechanisms of resistance to azole antifungal agents in Candida albicans strains displaying high-level fluconazole resistance isolated from human immunodeficiency virus-infected patients

Molecular mechanisms of azole resistance in Candida albicans, including alt erations in the target enzyme and increased efflux of drug, have been descr ibed, but the epidemiology of the resistance mechanisms has not been establ ished. We have investigated the molecular mechanisms of resistance to azole s in C albicans strains displaying high-level fluconazole resistance (MICs, greater than or equal to 64 mug/ml) isolated from human immunodeficiency v irus (HM-infected patients with oropharyngeal candidiasis. The levels of ex pression of genes encoding lanosterol 14 alpha -demethylase (ERG11) and eff lux transporters (MDR) and CDR) implicated in azole resistance were monitor ed in matched sets of susceptible and resistant isolates. In addition, ERG1 1 genes were amplified by PCR, and their nucleotide sequences were determin ed in order to detect point mutations with a possible effect in the affinit y for azoles. The analysis confirmed the multifactorial nature of azole res istance and the prevalence of these mechanisms of resistance in C. albicans clinical isolates exhibiting frank fluconazole resistance, with a predomin ance of overexpression of genes encoding efflux pumps, detected in 85% of a ll resistant isolates, being found. Alterations in the target enzyme, inclu ding functional amino acid substitutions and overexpression of the gene tha t encodes the enzyme, were detected in 65 and 35% of the isolates, respecti vely. Overall, multiple mechanisms of resistance were combined in 75% of th e isolates displaying high-level fluconazole resistance. These results may help in the development of new strategies to overcome the problem of resist ance as well as new treatments for this condition.