Yeast identification in the clinical microbiology accepted 15 August 2000 laboratory: phenotypical methods

Emerging yeast pathogens are favoured by increasing numbers of immunocompro mised patients and by certain current medical practices. These yeasts diffe r in their antifungal drug susceptibilities. and rapid species identificati on is imperative. A large variety of methods have been developed with the a im of facilitating rapid, accurate yeast identification. Significant recent commercial introductions have included species-specific direct enzymatic c olour tests, differential chromogenic isolation plates, direct immunologica l 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 identificati on 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 t ests for single species include the Bichrolatex Albicans and Krusei Color t ests, both immunologically based, as well as the Kernel Rapid Trehalose Ass imilation Broth for C. glabrata. Among broad-spectrum tests, the RapID Yeas t Plus system gives same-day identification of clinical yeasts, but perform ance depends on inoculum density and geographic isolate source. The API 20 C AUX system is considered a reference method, but newer systems such as Au xacolor and Fungichrom are as accurate and are more convenient. Among autom ated systems, the ID 32 C strip, the Vitek Yeast Biochemical Card and the V itek 2 ID-YST system correctly identify >93% of common yeasts, but the ID-Y ST is the most accurate with uncommon yeasts, including C. dubliniensis. Sp ectroscopic methods such as Fourier transformed-infrared spectroscopy offer potential advantages for the future. Overall, the advantages of rapid yeas t identification methods include relative simplicity and low cost. For all rapid methods, meticulous, standardized multicenter comparisons are needed before tests are fully accepted.