Genotyping of Vaginal Candida glabrata Isolates Using Microsatellite Marker Analysis and DNA Sequencing to Identify Mutations Associated with Antifungal Resistance

Abstract

Vulvovaginal candidosis is the second most common cause of vaginitis (17-39%) after bacterial vaginosis (22-50%). Since the diagnosis of vulvovaginal candidosis mainly depends on clinical findings without mycologic confirmatory tests and treated empirically, the actual incidence rate of vulvovaginal candidosis is unknown. Approximately 70-90% of vulvovaginal candidosis cases are caused by Candida albicans, however the increasing incidence of C.glabrata infections and its reduced susceptibility to azole drug therapy have generated increasing attention. The epidemiology and population structure of vulvovaginal candidosis due to C.glabrata are poorly characterized. This study was aimed to genotype the C.glabrata strains isolated from vaginal samples in Cukurova region, Turkey by microsatellite markers, to investigate the antifungal susceptibility profiles of the strains and to determine the molecular mechanisms leading to phenotypical azole resistance. A total of 34 unrelated vaginal C.glabrata strains isolated from patients with acute (n= 11) and recurrent (n= 14) vulvovaginal candidosis, control group (n= 9) without vaginitis symptoms, and a reference strain of C.glabrata CBS 138 (ATCC 2001) were included in the study. These isolates were genotyped using multiple-locus variable number tandem repeat analysis of three microsatellite markers (RPM2, MTI, and Cg6). Analysis of microsatellite markers was performed by fragment size determination of RPM2, MTI, and Cg6 PCR products through capillary electrophoresis. For each of the evaluated strains, DNA sequence analysis was performed for one gene (CgERG11) and four loci (CgPDR1, NTM1, TRP1, and URA3) to detect mutations possibly associated with antifungal resistance in each strain. In vitro susceptibility profiles of the strains to 13 antifungals and boric acid were determined according to CLSI document M27-A3 to investigate possible relationships between detected mutations and phenotypic resistance. C.glabrata CBS 138 strain was found to be susceptible to all the antifungals tested, while one of (%2.9) 34 vaginal C.glabrata isolates was found to be dose-dependent susceptible to fluconazole, 13 (38.2%) to itraconazole and 3 (8.8%) to voriconazole. No resistant strain were detected in the study population. Only three isolates were found to be resistant to clotrimazole (8.8%), however no relationship was identified between the genotypes and phenotypic resistance (p> 0.05). Thirteen genotypes were detected by microsatellite marker analysis, with high discrimination power (DP= 0.877). As a result, microsatellite marker analysis was validated as a rapid, reliable method for genotyping C.glabrata strains with good, but not optimal discriminatory power. Further studies examining larger numbers of isolates are needed to verify possible relationships between mutations and phenotypic resistance.