Low level of antifungal resistance of Candida glabrata blood isolates in Turkey: Fluconazole minimum inhibitory concentration and FKS mutations can predict therapeutic failure

Abstract

Background: Candida glabrata is the third leading cause of candidaemia in Turkey; however, the data regarding antifungal resistance mechanisms and genotypic diversity in association with their clinical implication are limited.

Objectives: To assess genotypic diversity, antifungal susceptibility and mechanisms of drug resistance of C glabrata blood isolates and their association with patients' outcome in a retrospective multicentre study.

Patients/methods: Isolates from 107 patients were identified by ITS sequencing and analysed by multilocus microsatellite typing, antifungal susceptibility testing, and sequencing of PDR1 and FKS1/2 hotspots (HSs).

Results: Candida glabrata prevalence in Ege University Hospital was twofold higher in 2014-2019 than in 2005-2014. Six of the analysed isolates had fluconazole MICs ≥ 32 µg/mL; of them, five harboured unique PDR1 mutations. Although echinocandin resistance was not detected, three isolates had mutations in HS1-Fks1 (S629T, n = 1) and HS1-Fks2 (S663P, n = 2); one of the latter was also fluconazole-resistant. All patients infected with isolates carrying HS-FKS mutations and/or demonstrating fluconazole MIC ≥ 32 µg/mL (except one without clinical data) showed therapeutic failure (TF) with echinocandin and fluconazole; seven such isolates were collected in Ege (n = 4) and Gulhane (n = 3) hospitals and six detected recently. Among 34 identified genotypes, none were associated with mortality or enriched for fluconazole-resistant isolates.

Conclusion: Antifungal susceptibility testing should be supplemented with HS-FKS sequencing to predict TF for echinocandins, whereas fluconazole MIC ≥ 32 µg/mL may predict TF. Recent emergence of C glabrata isolates associated with antifungal TF warrants future comprehensive prospective studies in Turkey.

Keywords: Candida glabrata; antifungal agents; candidaemia; drug resistance; genotype; molecular typing.

FIGURE 1

Mutations in the Pdr1p protein of Candida glabrata isolates. Amino acid changes observed in the isolates with high FLZ MIC values (≥32 µg/mL) are highlighted in orange colour. BD, DNA‐binding domain; MHD, middle homology domain; ID, inhibitory domain; and AD, activator domain

FIGURE 2

Minimum spanning tree illustrating the lack of clonal enrichment for isolates with FLZ MIC ≥ 32 µg/mL and/or mutations in HS1 of FKS1/2. All eight isolates, except for one without clinical data (marked red), showed azole and/or echinocandin TF