Gene Expression Analysis of Key Players Associated with Fluconazole Resistance in Candida albicans

Abstract

Background: Fluconazole resistance in Candida albicans has become a serious public health problem. Most previous studies have focused on deciphering the relationship between fluconazole resistance and amino acid substitutions in ERG11, which encodes cytochrome P450 lanosterol 14α-demethylase whose enzymatic activity is inhibited by azoles. However, azole resistance in C. albicans is a multifactorial phenomenon and several lines of evidence indicate that other genes and mechanisms may contribute to the development of fluconazole resistance. Objectives: The present study aimed to investigate the underlying role of six genes in fluconazole-resistant clinical strains of C. albicans, including ERG11, RTA2, and the efflux pump genes CDR1, CDR2, MDR1, and FLU1. Methods: We collected 40 fluconazole-resistant isolates and 40 susceptible isolates from patients with Candida infections in the First Affiliated Hospital of Nanchang University in China from 2005 to 2008. The susceptibility of the isolates to antifungal agents was tested by the M27-A3 broth microdilution method following the Clinical and Laboratory Standards Institute (CLSI) guidelines. Then, the gene expression levels of several key players in azole resistance were quantified. Results: Most fluconazole-resistant strains analyzed in this study were found to be cross-resistant to ketoconazole, itraconazole, and clotrimazole. We observed that the FLU1 gene expression significantly increased (P < 0.05) and exhibited major changes in most of the fluconazole-resistant isolates (75.0%). In addition, the expression of a novel gene, RTA2, was remarkably upregulated (P < 0.05). Interestingly, we found that 10% of the fluconazole-resistant isolates were simultaneously associated with ERG11 mutation and overexpression of RTA2, CDR1, and FLU1 genes. Unlike other studies, we did not find any difference in the expression of CDR2, MDR1, and ERG11 genes between the fluconazole-susceptible and resistant isolates. Conclusions: Our findings suggested that the overexpression of FLU1 and RTA2 genes may cause azole resistance; this finding had not been reported previously in clinical isolates of C. albicans. The upregulation of FLU1 and RTA2 genes was the predominant mechanism of fluconazole resistance in C. albicans in China.