Mechanisms of azole resistance among clinical isolates of Candida glabrata in Poland

Abstract

Candida glabrata is currently ranked as the second most frequently isolated aetiological agent of human fungal infections, next only to Candida albicans. In comparison with C. albicans, C. glabrata shows lower susceptibility to azoles, the most common agents used in treatment of fungal infections. Interestingly, the mechanisms of resistance to azole agents in C. albicans have been much better investigated than those in C. glabrata. The aim of the presented study was to determine the mechanisms of resistance to azoles in 81 C. glabrata clinical isolates from three different hospitals in Poland. The investigation was carried out with a Sensititre Yeast One test and revealed that 18 strains were resistant to fluconazole, and 15 were cross-resistant to all other azoles tested (voriconazole, posaconazole and itraconazole). One isolate resistant to fluconazole was cross-resistant to voriconazole, and resistance to voriconazole only was observed in six other isolates. All strains were found to be susceptible to echinocandins and amphotericin B, and five were classified as resistant to 5-fluorocytosine. The sequence of the ERG11 gene encoding lanosterol 14-a demethylase (the molecular target of azoles) of 41 isolates, including all strains resistant to fluconazole and three resistant only to voriconazole, was determined, and no amino acid substitutions were found. Real-time PCR studies revealed that 13 of 15 azole-resistant strains showed upregulation of the CDR1 gene encoding the efflux pump. No upregulation of expression of the CDR2 or ERG11 gene was observed.

Clonal Spread of Candida glabrata Bloodstream Isolates and Fluconazole Resistance Affected by Prolonged Exposure: a 12-Year Single-Center Study in Belgium

“…Our results indicate the coexpression of CgCDR1, CgPDH1, and CgSNQ2 in most of the isolates, previously attributed to their common transcription factor, CgPDR1 (11,12,43,45). However, only CgCDR1 was expressed at a significantly higher level in the FLC-resistant C. glabrata BSI isolates, indicating that it is the major FLC efflux pump in C. glabrata, consistent with previous studies (10,(41)(42)(43)45). Although significant, the higher expression of CgCDR1 in resistant strains was not marked and was generally lower than in previous reports (41,42,44), suggesting that other mechanisms are involved in FLC resistance in our set of isolates.…”

“…However, only CgCDR1 was expressed at a significantly higher level in the FLC-resistant C. glabrata BSI isolates, indicating that it is the major FLC efflux pump in C. glabrata, consistent with previous studies (10,(41)(42)(43)45). Although significant, the higher expression of CgCDR1 in resistant strains was not marked and was generally lower than in previous reports (41,42,44), suggesting that other mechanisms are involved in FLC resistance in our set of isolates. Indeed, gainof-function mutations in CgPDR1 were earlier reported to mediate azole resistance in C. glabrata (11)(12)(13)45), and genes other than those encoding ABC efflux pumps were shown to play a role in FLC resistance in C. glabrata.…”

ERG11 mutations associated with azole resistance in Candida albicans isolates from vulvovaginal candidosis patients

“…Azoles block fungal membrane formation [5]. Mutations in Erg11p can decrease the affinity of the target enzyme for azoles [6,7] . (ii) ERG11 overexpression also contributes to antifungal resistance.…”

Method-Dependent Epidemiological Cutoff Values for Detection of Triazole Resistance in Candida and Aspergillus Species for the Sensititre YeastOne Colorimetric Broth and Etest Agar Diffusion Methods

“…Some of those early studies also evaluated the agreement on the ranking of isolates within existent categorical endpoints with little attention to the critical issue of interlaboratory reproducibility. Recently, triazole MIC data for A. fumigatus and C. glabrata mutant strains obtained by these commercial methods have been reported (20)(21)(22)(23)(24). However, a lack of suitable clinical data has precluded the establishment of breakpoints (BPs) for the categorical interpretation of triazole MICs for either Candida or Aspergillus spp.…”