Routine use of a one minute trehalase and maltase test for the identification of Candida glabrata in four laboratories

Yeasts

Yeasts are unicellular organisms that reproduce mostly by budding and less often by fission. Most medically important yeasts originate from Ascomycota or Basidiomycota. Here, we review taxonomy, epidemiology, disease spectrum, antifungal drug susceptibility patterns of medically important yeast, laboratory diagnosis, and diagnostic strategies.

Candida glabrata: a deadly companion?

The yeast Candida glabrata has become a major fungal opportunistic pathogen of humans since the 1980s. Contrary to what its name suggests, it is much closer, phylogenetically, to the model yeast Saccharomyces cerevisiae than to the most prevalent human fungal pathogen, Candida albicans. Its similarity to S. cerevisiae fortunately extends to their amenability to molecular genetics methods. C. glabrata is now described as part of the Nakaseomyces clade, which includes two new pathogens and other environmental species. C. glabrata is likely a commensal species of the human digestive tract, but systemic infections of immunocompromised patients are often fatal. In addition to being the subject of active medical research, other studies on C. glabrata focus on fundamental aspects of evolution of yeast genomes and adaptation. For example, the genome of C. glabrata has undergone major gene and intron loss compared to S. cerevisiae. It is also an apparently asexual species, a feature that inevitably leads to questions about the species' evolutionary past, present and future. On-going research with this yeast continues to address various aspects of adaptation to the human host and mechanisms of evolution in the Saccharomycetaceae, major model organisms for biology.

Evaluation of the commercial rapid trehalose test (GLABRATA RTT) for the point of isolation identification of Candida glabrata isolates in primary cultures

Candidaemias account for 10-20% of nosocomial bloodstream infections depending on the study. Whilst Candida albicans remains the most frequently isolated species, Candida glabrata may be responsible for as many as 10-25% of all candidaemias. Moreover, C. glabrata is generally less susceptible to the azole antifungals than the majority of other pathogenic yeast species. Thus, a rapid test for the specific identification of isolates of C. glabrata would be useful for patient management if it could be performed at point of isolation, on primary cultures grown on standard mycological media directly from patient specimens. Under certain conditions, C. glabrata rapidly hydrolyses trehalose into glucose. The GLABRATA RTT kit allows detection of the preformed enzyme responsible for this action. This study has assessed GLABRATA RTT as an identification tool specifically at point of isolation. Sixty test isolates were evaluated: 39 clinical isolates of C. glabrata identified at the UK Mycology Reference Laboratory, examples of the recently described genetic relatives of C. glabrata, Candida nivariensis (n = 6) and Candida bracarensis (n = 1), and a selection of other common pathogenic yeast species (n = 14). The test provided results within 30 min. Although 77% (30/39) of confirmed C. glabrata isolates were correctly identified by GLABRATA RTT (positive trehalase test), 23% (9/39) of isolates gave negative or equivocal results. All other yeast species gave negative results. The performance of GLABRATA RTT in this study is compared to previous evaluations of the test which employed isolates pre-cultured on specialised media and to other existing conventional identification methodologies.

Identification of Candida albicans and Candida glabrata within 1.5 hours directly from positive blood culture bottles with a shortened peptide nucleic acid fluorescence in situ hybridization protocol

Candida albicans and Candida glabrata can be identified in blood culture bottles within 2.5 h using peptide nucleic acid fluorescence in situ hybridization. A 1.25-h protocol was compared to the standard with 40 positive (clinical and spiked) blood culture bottles tested in batches of 5. All C. albicans (15) and C. glabrata (16) isolates, alone or mixed, were identified correctly using both protocols, whereas 18 isolates (five other species) were negative by both protocols. This shortened method will significantly reduce the time to identification.

Yeast identification--past, present, and future methods

The focus of this review is the evolution of biochemical phenotypic yeast identification methods with emphasis on conventional approaches, rapid screening tests, chromogenic agars, comprehensive commercial methods, and the eventual migration to genotypic methods. As systemic yeast infections can be devastating and resistance is common in certain species, accurate identification to the species level is paramount for successful therapy and appropriate patient care.

Biology of the pathogenic yeast Candida glabrata

The yeasts, being favorite eukaryotic microorganisms used in food industry and biotechnologies for production of biomass and various substances, are also used as model organisms in genetic manipulation, molecular and biological research. In this respect, Saccharomyces cerevisiae is the best-known species but current situation in medicine and industry requires the use of other species. Here we summarize the basic taxonomic, morphological, physiological, genetic, etc. information about the pathogenic yeast Candida glabrata that is evolutionarily very closely related to baker's yeast.

Routine use of a commercial test, GLABRATA RTT, for rapid identification of Candida glabrata in six laboratories

When evaluated in six clinical laboratories from six countries with 1,174 fresh isolates, including 715 Candida glabrata and 459 non-C. glabrata strains, GLABRATA RTT (Fumouze Diagnostics, Levallois Perret, France) yielded an overall sensitivity and an overall specificity of 95.8 and 98.9%, respectively. The results were consistent from one laboratory to another. The five false-positive results corresponded to C. parapsilosis (n = 2), C. tropicalis, C. guilliermondii, and C. lusitaniae. GLABRATA RTT allows a rapid, cost-effective, and reliable presumptive identification of C. glabrata.