Mutations and/or Overexpressions of ERG4 and ERG11 Genes in Clinical Azoles-Resistant Isolates of Candida albicans.

Objective: We aimed to investigate whether mutations and/or overexpressions of ERG4 and ERG11 genes were involved in drug resistance to azoles in Candida albicans.

Methods: Totally, 34 clinical isolates of C. albicans were included in this study. Antimicrobial susceptibility tests, including 5-fluorocytosine (5-FC), amphotericin B (AMB), fluconazole (FCA), itraconazole (ITR), and voriconazole (VRC), were performed by broth microdilution method. Mutations in the ERG4 and ERG11 genes sequence were detected. The messenger RNA (mRNA) levels of ERG4 and ERG11 were measured by quantitative real-time polymerase chain reaction. The correlation of the expression levels of ERG4 with ERG11 genes in susceptible isolates and resistant isolates was analyzed by Pearson's correlation analysis.

Results: Among 34 C. albicans isolates, 52.94%, 70.59%, and 50.00% isolates were resistant to FCA, ITR, and VRC, respectively. Sequencing results revealed that only 2 silent mutations were found in ERG4 gene, while 10 amino acid substitutions, including 6 reported previously and 4 new identified, were frequently found in ERG11 gene. The mRNA levels of ERG4 and ERG11 genes were significantly elevated in resistant compared with susceptible C. albicans isolates. Furthermore, the mRNA level of ERG4 was positively correlated with ERG11 in susceptible but not resistant C. albicans isolates.

Conclusions: The resistance to azoles may be associated with the mutations in ERG11 but not ERG4 gene in C. albicans isolates. In addition, overexpressed ERG4 and ERG11 genes are found in resistant C. albicans isolates, and the mRNA levels of ERG4 may be irrelevant to ERG11 in resistant C. albicans isolates.