Expression Pattern of Drug-Resistance Genes in Candida Albicans at Different Fluconazole Concentrations

Abstract

Candida albicans is an opportunistic fungus that is part of the normal flora of our gastrointestinal and urinary tracts, but can cause infections in immune compromised individuals. Fluconazole (FLC), which is a fungistatic azole, is a common drug used for treatment of C. albicans infection by targeting lanosterol demethylase (ERG11). Some clinical isolates show resistance to FLC, which can be attributed to an over expression of ABC transporters (CDR1, CDR2), Major Facilitator Transporter (MDR1), and the azole target (ERG11). Commonly the expression pattern of these genes is compared across strains of susceptible and resistant strains in the absence of drugs. However, gene expression levels of each strain may be different in different drug doses. This study investigates the pattern of gene expression of MDR1, CDR1, CDR2, and ERG11 in different C. albicans matched isolates at different doses of FLC. Along with the wildtype strain SC5314, isolates from a single patient with varying susceptibility to FLC were selected. The Minimum Inhibitory Concentration (MIC80) to FLC for each strain was determined by microbroth dilution. The mRNA expression of the genes was analyzed using Quantitative Real-Time PCR (qRT-PCR) at FLC concentrations 4-fold lower, 4- fold higher, and at their respective MICs. Gene expression was analyzed with and without FLC induction and the MDR1/CDR1/CDR2/ERG11 gene expression levels of all the strains were normalized to their uninduced expression levels. The experiments show that in resistant strains, the genes MDR1 and ERG11 are over expressed even without FLC induction, consistent with previous work. Increasing the FLC concentration does not have any significant effect on gene expression in resistant strains. For the azolesusceptible strains, the gene expression of CDR1 and CDR2 increases at FLC concentration below its MIC80 and declines at concentrations above the MIC80. Hence, the gene expressions of clinical isolates vary according to their MIC80 values.