Prevalence of Molecular Mechanisms of Resistance to Azole Antifungal Agents in <i>Candida albicans</i> Strains Displaying High-Level Fluconazole Resistance Isolated from Human Immunodeficiency Virus-Infected Patients

TLDR

Azole resistance in Candida albicans involves target enzyme alterations and increased drug efflux, yet the epidemiology of these mechanisms remains unclear. This study examined the molecular mechanisms underlying high‑level fluconazole resistance in Candida albicans isolates from HIV‑infected patients with oropharyngeal candidiasis. We quantified expression of ERG11, MDR1, and CDR genes and sequenced ERG11 to identify point mutations in matched susceptible and resistant isolates. The analysis revealed that 85 % of resistant isolates overexpressed efflux pumps, 65 % had target‑enzyme mutations, 35 % overexpressed ERG11, and 75 % combined multiple mechanisms, underscoring the multifactorial nature of resistance and guiding future therapeutic strategies.

Abstract

ABSTRACT Molecular mechanisms of azole resistance in Candida albicans , including alterations in the target enzyme and increased efflux of drug, have been described, but the epidemiology of the resistance mechanisms has not been established. We have investigated the molecular mechanisms of resistance to azoles in C. albicans strains displaying high-level fluconazole resistance (MICs, ≥64 μg/ml) isolated from human immunodeficiency virus (HIV)-infected patients with oropharyngeal candidiasis. The levels of expression of genes encoding lanosterol 14α-demethylase ( ERG11 ) and efflux transporters ( MDR1 and CDR) implicated in azole resistance were monitored in matched sets of susceptible and resistant isolates. In addition, ERG11 genes were amplified by PCR, and their nucleotide sequences were determined in order to detect point mutations with a possible effect in the affinity for azoles. The analysis confirmed the multifactorial nature of azole resistance and the prevalence of these mechanisms of resistance in C. albicans clinical isolates exhibiting frank fluconazole resistance, with a predominance of overexpression of genes encoding efflux pumps, detected in 85% of all resistant isolates, being found. Alterations in the target enzyme, including functional amino acid substitutions and overexpression of the gene that encodes the enzyme, were detected in 65 and 35% of the isolates, respectively. Overall, multiple mechanisms of resistance were combined in 75% of the isolates displaying high-level fluconazole resistance. These results may help in the development of new strategies to overcome the problem of resistance as well as new treatments for this condition.