Soledad Gamarra

Requirement for Ergosterol in V-ATPase Function Underlies Antifungal Activity of Azole Drugs

Ergosterol is an important constituent of fungal membranes. Azoles inhibit ergosterol biosynthesis, although the cellular basis for their antifungal activity is not understood. We used multiple approaches to demonstrate a critical requirement for ergosterol in vacuolar H+-ATPase function, which is known to be essential for fungal virulence. Ergosterol biosynthesis mutants of S. cerevisiae failed to acidify the vacuole and exhibited multiple vma − phenotypes. Extraction of ergosterol from vacuolar membranes also inactivated V-ATPase without disrupting membrane association of its subdomains. In both S. cerevisiae and the fungal pathogen C. albicans, fluconazole impaired vacuolar acidification, whereas concomitant ergosterol feeding restored V-ATPase function and cell growth. Furthermore, fluconazole exacerbated cytosolic Ca2+ and H+ surges triggered by the antimicrobial agent amiodarone, and impaired Ca2+ sequestration in purified vacuolar vesicles. These findings provide a mechanistic basis for the synergy between azoles and amiodarone observed in vitro. Moreover, we show the clinical potential of this synergy in treatment of systemic fungal infections using a murine model of Candidiasis. In summary, we demonstrate a new regulatory component in fungal V-ATPase function, a novel role for ergosterol in vacuolar ion homeostasis, a plausible cellular mechanism for azole toxicity in fungi, and preliminary in vivo evidence for synergism between two antifungal agents. New insights into the cellular basis of azole toxicity in fungi may broaden therapeutic regimens for patient populations afflicted with systemic fungal infections.

Fitness and Virulence Costs of Candida albicans FKS1 Hot Spot Mutations Associated With Echinocandin Resistance

The identification of FKS1 mutations in Candida albicans associated with echinocandin resistance has raised concerns over the spread of drug-resistant strains. We studied the impact of fks1 mutations on C. albicans virulence and fitness. Compared with wild-type strains for FKS1, echinocandin-resistant C. albicans strains with homozygous fks1 hot-spot mutations had reduced maximum catalytic capacity of their glucan synthase complexes and thicker cell walls attributable to increased cell wall chitin content. The fks1 mutants with the highest chitin contents had reduced growth rates and impaired filamentation capacities. Fks1 mutants were hypovirulent in fly and mouse models of candidiasis, and this phenotype correlated with the cell wall chitin content. In addition, we observed reduced fitness of echinocandin-resistant C. albicans in competitive mixed infection models. We conclude that fks1 mutations that confer echinocandin resistance come at fitness and virulence costs, which may limit their epidemiological and clinical impact.

Mechanism of the Synergistic Effect of Amiodarone and Fluconazole in Candida albicans

ABSTRACT The antiarrhythmic drug amiodarone has been found to have fungicidal activity. In Saccharomyces cerevisiae, its antifungal activity is mediated by calcium overload stress, which leads to a rapid nuclear accumulation of the calcineurin-regulated transcription factor CRZ1. In addition, low doses of amiodarone have been reported to be synergistic with fluconazole in fluconazole-resistant Candida albicans. To establish its mechanism of toxicity in C. albicans, we used expression profiling of key pathway genes to examine cellular responses to amiodarone alone and in combination with fluconazole. Gene expression profiling of 59 genes was done in five C. albicans strains (three fluconazole-susceptible strains and two fluconazole-resistant strains) after amiodarone and/or fluconazole exposure. Of the 59 genes, 27 analyzed showed a significant change (>2-fold) in expression levels after amiodarone exposure. The up- or downregulated genes included genes involved in Ca2+ homeostasis, cell wall synthesis, vacuolar/lysosomal transport, diverse pathway regulation, stress response, and pseudohyphal morphogenesis. As expected, fluconazole induces an increase in ergosterol pathway genes expression levels. The combination treatment significantly dampened the transcriptional response to either drug, suggesting that synergism was due to an inhibition of compensatory response pathways. This dampening resulted in a decrease in total ergosterol levels and decreased pseudohyphal formation, a finding consistent with decreased virulence in a murine candidiasis model.

Set of Classical PCRs for Detection of Mutations in Candida glabrata FKS Genes Linked with Echinocandin Resistance

ABSTRACT Clinical echinocandin resistance among Candida glabrata strains is increasing, especially in the United States. Antifungal susceptibility testing is considered mandatory to guide therapeutic decisions. However, these methodologies are not routinely performed in the hospital setting due to their complexity and the time needed to obtain reliable results. Echinocandin failure in C. glabrata is linked exclusively to Fks1p and Fks2p amino acid substitutions, and detection of such substitutions would serve as a surrogate marker to identify resistant isolates. In this work, we report an inexpensive, simple, and quick classical PCR set able to objectively detect the most common mechanisms of echinocandin resistance in C. glabrata within 4 h. The usefulness of this assay was assessed using a blind collection of 50 C. glabrata strains, including 16 FKS1 and/or FKS2 mutants.

First itraconazole resistant "Aspergillus fumigatus" clinical isolate harbouring a G54E substitution in Cyp51Ap in South America

BACKGROUND A 27-year-old male rural worker was admitted with a fungal keratitis due to an injury involving plant detritus. MATERIALS AND METHODS Specimens were collected for microscopy examination and culture. The isolate was identified by morphological and molecular criteria. Susceptibility testing was performed using CLSI methods. CYP51A gene was PCR amplified and sequenced. RESULTS An Aspergillus fumigatus strain resistant to itraconazole (MIC>8μg/ml) was isolated. The isolate was susceptible to amphotericin B, posaconazole, voriconazole and caspofungin. CYP51A sequencing showed two mutations leading on the G54E substitution. The patient received natamycin as treatment. CONCLUSIONS This is the first report in South America of a clinical A. fumigatus strain carrying the substitution G54E at Cyp51Ap associated with itraconazole resistance. Considering the patient was azole-naive, this resistant isolate may have been acquired from the environment.

Quick Detection of FKS1 Mutations Responsible for Clinical Echinocandin Resistance in Candida albicans

ABSTRACT A rapid molecular-based assay for the detection of the Candida albicans FKS1 gene mutations responsible for resistance to echinocandin drugs was designed and evaluated. The assay consisted of a multiplexed PCR set of 5 tubes able to detect the most commonly described resistance mechanism, including FKS1 hot spot 1 and hot spot 2 mutations. The performance and specificity of the assay was evaluated using a double-blinded panel of 50 C. albicans strains. The assay showed a sensitivity of 96% and was able to detect all homozygous mutants included in the collection of strains, demonstrating that it is a robust, quick, and labor-saving method that is suitable for a routine clinical diagnostic laboratory.

Molecular confirmation of the relationship between Candida guilliermondii Fks1p naturally occurring amino acid substitutions and its intrinsic reduced echinocandin susceptibility.

ABSTRACT Candida guilliermondii shows intrinsic reduced echinocandin susceptibility. It harbors two polymorphisms (L633M and T634A) in the Fks1p hot spot 1 region. Our objective was to confirm that the reduced echinocandin susceptibility of C. guilliermondii is due to those naturally occurring substitutions. We constructed a Saccharomyces cerevisiae mutant in which a region of the FKS1 gene (including hot spot 1) was replaced with that from C. guilliermondii. The chimeric mutants showed 32-fold increases in echinocandin MIC values, confirming the hypothesis.

Single-tube classical PCR for Candida auris and Candida haemulonii identification

BACKGROUND Candida auris and Candida haemulonii are emerging and multiresistant pathogens. C. auris has produced hospital outbreaks and is misidentified by phenotypic-based methods. The only reliable identification methods are DNA sequencing and MALDI-TOF. AIMS To develop a classical-PCR method capable of rapidly and accurately identify C. auris and C. haemulonii. METHODS A multiplex PCR was carried out in one tube that included an internal control and oligonucleotides that specifically hybridize to the ITS2 region of C. auris and C. haemulonii. The usefulness of the new method was verified by testing a collection of 50 strains of 20 different species (previously identified by ITS sequencing). The selection of species was made in order to emulate the C. auris panel used by the CDC to validate diagnostic tools. In addition, other yeast species not included in the aforementioned panel were incorporated based on reported identification errors. RESULTS The results obtained with the proposed protocol were in total agreement with those obtained by ITS sequencing. CONCLUSIONS We present a PCR method able to unequivocally identify C. auris and differentiate it from C. haemulonii. It is inexpensive, fast and it could be a useful tool to reduce the chances of a C. auris outbreak.

Multiplex PCR designed to differentiate species within the Candida glabrata complex

BACKGROUND No phenotypic methods are available to unequivocally differentiate species within the Candida glabrata complex. AIMS To develop a new multiplex PCR method to differentiate between the three species of the C. glabrata species complex, as well as using it to study a C. glabrata collection to discover strains of the newly described species. METHODS The method was developed based on the Internal Transcribed Spacer (ITS) sequence differences between the species. It was validated by using a blinded collection of strains and, finally, the new molecular method was used to study a collection of 192 C. glabrata species complex strains. The obtained results were compared with ITS sequencing. RESULTS The proposed method showed 100% concordance with ITS sequencing and proved to be effective for clinical and epidemiological applications. Two Candida bracarensis and three Candida nivariensis were found out of the 192 studied strains (0.93% and 1.40% prevalence, respectively). CONCLUSIONS A fast, inexpensive, robust and highly reproducible multiplex PCR method is presented. Its usefulness is demonstrated by studying a large collection of C. glabrata sensu lato strains.

beta-Thalassaemia Major in a Spanish Patient due to a Compound Heterozygosity for CD39 C --> T/-28 A --> C.

A Spanish male patient with β-thalassaemia major was studied. Compound heterozygosity was found for one of the most common β-globin gene mutations in the Spanish population (codon 39 C → T) and for a mutation in the TATA box element of the β-globin gene promoter (−28 A → C mutation). To our knowledge this is the first report of a CD39 C → T and −28 A → C change association and the first report of the −28 A → C substitution in a Spanish patient.