Azole resistance in Candida glabrata: coordinate upregulation of multidrug transporters and evidence for a Pdr1-like transcription factor

Rapid identification of Candida species and other clinically important yeast species by flow cytometry

Two rapid diagnostic assays, utilizing two different Luminex flow cytometry methods, were developed for identification of clinically important ascomycetous yeast species. Direct hybridization and allele-specific primer extension methods were both successful in establishing a DNA-based assay that can rapidly and accurately identify Candida albicans, Candida krusei, Candida parapsilosis, Candida glabrata, and Candida tropicalis as well as other clinical species. The direct hybridization assay was designed to identify a total of 19 ascomycetous yeast species, and the allele-specific primer extension assay was designed to identify a total of 34 species. Probes were validated against 438 strains representing 303 species. From culture to identification, the allele-specific primer extension method takes 8 h and the direct hybridization method takes less than 5 h to complete. These assays represent comprehensive, rapid tests that are well suited for the clinical laboratory.

Promoter-dependent disruption of genes: simple, rapid, and specific PCR-based method with application to three different yeast

PCR product-based gene disruption has greatly accelerated molecular analysis of Saccharomyces cerevisiae. This approach involves amplification of a marker gene (e.g., URA3) including its flanking regulatory (promoter and polyadenylation) regions using primers that include at their 5' ends about 50 bases of homology to the targeted gene. Unfortunately, this approach has proved less useful in organisms with higher rates of non-homologous recombination; e.g., in the yeast Candida glabrata, desired recombinants represent < or =2% of transformants. We modified the PCR-based approach by eliminating marker-flanking regions and precisely targeting recombination such that marker expression depends on the regulatory sequences of the disrupted gene. Application of this promoter-dependent disruption of genes (PRODIGE) method to three C. glabrata genes (SLT2, LEM3, and PDR1) yielded desired recombinants at frequencies of 20, 31, and 11%, the latter representing a weakly expressed gene. For Candida albicans LEM3 and RHO1, specificity was 79-95% for one or both alleles, >sixfold higher than the published results with conventional PCR-based gene disruption. All 5 C. glabrata and C. albicans mutants had predicted phenotypes of calcofluor hypersensitivity (slt2Delta and RHO1/rho1Delta), cycloheximide hypersensitivity (pdr1Delta), or miltefosine resistance (lem3Delta and lem3Delta/lem3Delta). PRODIGE application to the S. cerevisiae PDR5 gene in strains with and without the Pdr1-Pdr3 transcriptional activators of this gene confirmed that transformant yield and growth rate depend on promoter strength. Using this PDR5 promoter-URA3 recombinant, we further demonstrate a simple extension of the method that yields regulatory mutants via 5-fluoroorotic acid selection. PRODIGE warrants testing in other yeast, molds, and beyond.

A yeast by any other name: Candida glabrata and its interaction with the host

Well-characterized traits important to Candida albicans virulence, such as hyphal formation or secreted proteinase activity, play no known role in Candida glabrata virulence. Likewise, some C. glabrata characteristics, such as chromatin-based regulation of the large telomeric family of lectins encoded by the EPA (epithelial adhesin) genes, have no precise parallels in C. albicans. However, similarities between the two species, for example in population structure, in the large numbers of (putative) adhesins that they encode, and in phenotypic plasticity conferred by phenotypic switching, suggest that they share general strategies in adaptation to an opportunistic lifestyle.

Candida glabrata is unusual with respect to its resistance to cationic antifungal proteins

Naturally occurring salivary antifungal proteins have been of major interest, due to their potential to provide the basis for peptide antimycotics effective in combating fungal infections in the oral cavity or elsewhere. We tested the fungistatic activity of a number of cationic antifungal proteins, with major emphasis on histatin 5, a basic protein secreted by the human parotid and submandibular glands. Histatin 5 inhibited the growth of Candida albicans and that of other medically important Candida species, such as C. kefyr, C. krusei, and C. parapsilosis, with IC50 values in the range of 10-20 microg/ml. Two Cryptococcus neoformans strains were also sensitive (IC50 5.2 and 5.6 microg/ml). On the other hand, three C. glabrata strains (ATCC 90030, 2001 and 64677) were entirely insensitive to histatin 5 (IC50>225 microg/ml). Four genetically very similar species to C. glabrata, Candida castelli (CBS 4332), Saccharomyces cerevisiae (S288C, BY4741 and CBS 1171), Kluyveromyces delphensis (CBS 2170) and Kluyveromyces bacillisporus (CBS 7720) were all sensitive to histatin 5 (IC50 2.6-64.6 microg/ml). C. glabrata was also insensitive to other members of the histatin family; histatin 1, 3 and P-113 (IC50 values in all cases >225 microg/ml). In addition, two entirely different cationic antifungal proteins originating from frog skin, PGLa and magainin 2, also showed a strong reduced activity toward this fungus. Besides the well-described inherent resistance of C. glabrata to azole-derived antifungal agents, our studies indicate that this species is also able to withstand the otherwise detrimental activities of cationic antifungal proteins.