Rapid methods for identification of the most frequent clinical yeasts.

Over the past several decades there has been a significant increase in the number of fungal diseases. Although infections can occur in normal hosts, most of them are seen in patients who are immunosuppressed or immunocompromised such as those with AIDS or who have received transplants, corticoids or anticancer drugs [1]. Other predisposing factors responsible for yeast infections include overuse of broad-spectrum antibiotics, the presence of indwelling catheters, and intravenous drug abuse. In these opportunistic infections, due to microorganisms from endogenous or exogenous sources, an increasing diversity of opportunistic yeasts are implicated. The yeasts most commonly isolated from clinical specimens, in decreasing order of occurrence, include Candida albicans, Candida glabrata, Candida tropicalis, Candida parapsilosis, Saccharomyces spp, Candida krusei, Candida guilliermondii, Rhodotorula spp, Trichosporon spp and Cryptococcus neoformans [2]. However, C. albicans remains the most common species isolated, representing about 60% of all clinical isolates of yeasts [3]. In addition, opportunistic yeasts demonstrate various degrees of resistance in vivo and in vitro to common antifungal agents [4] and it is well-known that strains of Candida lusitaniae [5] on the one hand and C. krusei and C. glabrata [6-8] on the other are relatively resistant to amphotericin B and fluconazole, respectively. Consequently, mycoses are a growing medical problem requiring prompt diagnosis and early antifungal therapy. There are a variety of methods available for identifying yeasts from clinical specimens. These include (i) conventional methods, e.g. the germ tube test, morphology studies, and carbohydrate utilization; (ii) rapid methods, e.g. enzymatic tests on colonies after primary isolation or directly on differential medium, latex agglutination tests and molecular biology based methods, and (iii) commercially available methods, e.g. manual biochemical panels (with carbohydrate assimilation and/ or fermentation and/ or enzyme profiles) and automated systems. This paper review the methods for rapid identification of yeasts, i.e., methods requiring less than five hours after isolation. These rapid methods has been mainly developed for Candida species identification but several rapid tests can also be used for the identification of C. neoformans.