Yeast identification in the clinical microbiology laboratory: phenotypical methods

Abstract

Emerging yeast pathogens are favoured by increasing numbers of immunocompromised patients and by certain current medical practices. These yeasts differ in their antifungal drug susceptibilities, and rapid species identification is imperative. A large variety of methods have been developed with the aim of facilitating rapid, accurate yeast identification. Significant recent commercial introductions have included species-specific direct enzymatic colour tests, differential chromogenic isolation plates, direct immunological tests, and enhanced manual and automated biochemical and enzymatic panels. Chromogenic isolation media demonstrate better detection rates of yeasts in mixed cultures than traditional media, and allow the direct identification of Candida albicans by means of colony colour. Comparative evaluation of rapid methods for C. albicans identification, including the germ tube test, shows that chromogenic media may be economically advantageous. Accurate tests for single species include the Bichrolatex Albicans and Krusei Color tests, both immunologically based, as well as the Remel Rapid Trehalose Assimilation Broth for C. glabrata. Among broad-spectrum tests, the RapID Yeast Plus system gives same-day identification of clinical yeasts, but performance depends on inoculum density and geographic isolate source. The API 20 C AUX system is considered a reference method, but newer systems such as Auxacolor and Fungichrom are as accurate and are more convenient. Among automated systems, the ID 32 C strip, the Vitek Yeast Biochemical Card and the Vitek 2 ID-YST system correctly identify >93% of common yeasts, but the ID-YST is the most accurate with uncommon yeasts, including C. dubliniensis. Spectroscopic methods such as Fourier transformed-infrared spectroscopy offer potential advantages for the future. Overall, the advantages of rapid yeast identification methods include relative simplicity and low cost. For all rapid methods, meticulous, standardized multicenter comparisons are needed before tests are fully accepted.

Potentially pathogenic yeast isolated from the throat and cloaca of an Arctic colonial seabird: the little auk (Alle alle)

“…Once proliferated, the fungi were passaged onto solid media [Nickerson's medium modified according to Dynowska and Kisicka 2005a, b; with broth bouillon and serum in a proportion of 1:1)] to visualize diagnostic traits (morphology, arrangement of the colony, and colors). Additionally, for diagnostic purposes, biochemical tests using standard strips (API 20C, API 20AUX, bioMérieux, France) were performed to analyze the assimilation and fermentation capacity of particular fungi (Freydiere et al 2001). The following literature was used to identify the fungi species: Kreger-van Rij (1984), De Hoog et al (2000), Kurtzman and Fell (2000), Howard (2003) and Kurtzman et al (2011).…”

Bacterial and fungal colonization of burn wounds

“…Fungal cultures were obtained on Sabouraud dextrose agar (Difco) and on "mycogel" agar (Oxoid) at 37°C and observed daily for 20 days. The characterization of fungi was done by the germ tube test, morphological examination and automated method Vitek YBC yeast identification system (bioMérieux Vitek, Inc., MI, US) (Freydiere et al 2001). However, antibiotic sensitivity of fungi can not be done due to technical problems.…”

Raman spectroscopic identification of single yeast cells

“…Various conventional methods, e.g. enzymatic tests, exist that allow for an identification of yeast cells in about 5 h. 1 However, these tests require a pure culture or are not available for all species.…”