Related Experiment Video
Updated: Jun 12, 2026
Whole Genome Sequencing of Candida glabrata for Detection of Markers of Antifungal Drug Resistance
Published on: December 28, 2017
Microarray and molecular analyses of the azole resistance mechanism in Candida glabrata oropharyngeal isolates
Huei-Fung Tsai1, Lindsay R Sammons, Xiaozhen Zhang
1Clinical Mycology Section, Laboratory of Clinical Infectious Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA.
Abstract:
DNA microarrays were used to analyze Candida glabrata oropharyngeal isolates from seven hematopoietic stem cell transplant recipients whose isolates developed azole resistance while the recipients received fluconazole prophylaxis. Transcriptional profiling of the paired isolates revealed 19 genes upregulated in the majority of resistant isolates compared to their paired susceptible isolates. All seven resistant isolates had greater than 2-fold upregulation of C. glabrata PDR1 (CgPDR1), a master transcriptional regulator of the pleiotropic drug resistance (PDR) network, and all seven resistant isolates showed upregulation of known CgPDR1 target genes. The altered transcriptome can be explained in part by the observation that all seven resistant isolates had acquired a single nonsynonymous mutation in their CgPDR1 open reading frame. Four mutations occurred in the regulatory domain (L280P, L344S, G348A, and S391L) and one in the activation domain (G943S), while two mutations (N764I and R772I) occurred in an undefined region. Association of azole resistance and the CgPDR1 mutations was investigated in the same genetic background by introducing the CgPDR1 sequences from one sensitive isolate and five resistant isolates into a laboratory azole-hypersusceptible strain (Cgpdr1 strain) via integrative transformation. The Cgpdr1 strain was restored to wild-type fluconazole susceptibility when transformed with CgPDR1 from the susceptible isolate but became resistant when transformed with CgPDR1 from the resistant isolates. However, despite the identical genetic backgrounds, upregulation of CgPDR1 and CgPDR1 target genes varied between the five transformants, independent of the domain locations in which the mutations occurred. In summary, gain-of-function mutations in CgPDR1 contributed to the clinical azole resistance, but different mutations had various degrees of impact on the CgPDR1 target genes.
Insights
Gain-of-function mutations in Candida glabrata PDR1 (CgPDR1) drive azole resistance in hematopoietic stem cell transplant patients. Different CgPDR1 mutations impact drug resistance gene expression variably, contributing to clinical fluconazole resistance.
Area of Science:
- Medical Mycology
- Molecular Biology
- Antimicrobial Resistance
Background:
- Azole antifungal resistance is a growing concern in immunocompromised patients.
- Candida glabrata is a common cause of oropharyngeal infections, particularly in hematopoietic stem cell transplant (HSCT) recipients.
- Fluconazole prophylaxis is standard for HSCT patients but can select for resistant strains.
Purpose of the Study:
- To investigate the molecular mechanisms underlying azole resistance in Candida glabrata isolates from HSCT patients.
- To identify specific genetic alterations, particularly in the CgPDR1 gene, associated with acquired fluconazole resistance.
- To determine the functional impact of CgPDR1 mutations on gene expression and antifungal susceptibility.
Main Methods:
- DNA microarrays for transcriptional profiling of paired susceptible and resistant Candida glabrata isolates.
- Whole-genome sequencing to identify mutations in the CgPDR1 gene.
- Integrative transformation experiments to assess the effect of CgPDR1 mutations in a defined genetic background.
Main Results:
- Transcriptional profiling revealed upregulation of 19 genes in resistant isolates, including C. glabrata PDR1 (CgPDR1) and its target genes.
- All seven resistant isolates harbored a nonsynonymous mutation in CgPDR1, with four in the regulatory domain, one in the activation domain, and two in an undefined region.
- Transforming a hypersusceptible strain with CgPDR1 from resistant isolates conferred azole resistance, confirming the role of these mutations.
Conclusions:
- Gain-of-function mutations in CgPDR1 are a significant contributor to clinical azole resistance in Candida glabrata.
- Different CgPDR1 mutations exhibit varying degrees of impact on the expression of CgPDR1 target genes and overall drug resistance.
- Understanding CgPDR1 mutation-specific effects is crucial for managing azole-resistant Candida infections in vulnerable patient populations.
