Evaluation of a modified dye pour-plate auxanographic method for the rapid identification of clinically significant yeasts. Comparison with two commercial systems

Conventional and rapid methods for yeast identification

Identification of yeasts depends on data obtained from morphological features and physiological characteristics. This article reviews the commonly used conventional methods for the identification of yeast to set the stage for a critical review of rapid systems for yeast identification. Comparative analyses of percentage agreement of API 20C, Uni-Yeast Tek, Minitek, Mycotube, Micro-Drop, Auxodisk, Iatron, Autobac 1, AMS, Abbott MS-2, and Abbott Quantum 11 against the conventional method and, in some cases, against each other are tabulated. Gas liquid chromatography method, enzyme method, MUG, and the Fung's mini-system are also mentioned as possible rapid methods for yeast identification. The purpose of this review is to update the rapidly expanding information concerning diagnostic kits and systems for yeast identification and analyze some of the advantages, disadvantages and potential uses of rapid systems of yeast identification.

Rapid identification of yeasts by semi-automated and conventional methods

Five different methods for the identification of significant yeast from clinical specimens were compared for their reliability, rapidity and cost-effectiveness. Three commercial methods consisted of semi-automated Abbott's yeasts identification system using MS-2 (Abbott Laboratories, Diagnostic Division, Irving, Texas), API 20C (Analytab Products, Inc., Plainview, NY) and Uni-Yeast-Tek (Flow Labs, Inc., MacLean, VA). Two conventional methods included the modified dye-plur plate auxanographic and rapid tube assimilation method. The 242 coded clinical isolates used in this study included 20 species of Candida, Cryptococcus, Saccharomyces Geotrichum, Rhodotorula, Torulopsis and Trichosporon. The identification accuracies with all the systems ranges between 92.3% to 97.5%. Results were available with Abbott's MS-2 within 24 h, with rapid tube assimilation method in 6-48 h and in 72 h with other systems. Rapid tube assimilation and dye-pour-plate auxanographic methods were least expensive, with labour and material costing around $1.00 per identification, whereas the commercial system cost a little over $5.00.

The systems approach to diagnostic microbiology

"Classical" and "conventional" methods for microbial identification are still utilized in clinical microbiology laboratories; however, significant advances in methodology have taken place in the last two decades. In the transition from classical to contemporary methodologies, the reference point has changed from multistep procedures to unitary procedures with marked emphasis on standardization, speed, reproducibility, and most recently, mechanization and automation. The most evident expression of this transition is the adaptation or streamlining of classical methods in the form of "miniaturized identification systems" and their commercial availability. This review analyzes the development of the underlining principles that make the systems approach to diagnostic microbiology possible.

Suitability of the modified API 20 C, Mycotube and Bacto-Candida-albicans-Antiserum for the identification of yeasts in the routine laboratory

In a clinical routine study 304 yeasts were examined with the aid of API 20 C Auxanogram (Analytab Products Inc.) Mycotube (Roche) and Bacto-Candida-albicans-Antiserum (Difco) (=CAA). API (in parenthesis the result of the Mycotube test) identified 99% (92.4%) correctly; without considering C. albicans, the result was correct in 96.5% (75.8%). The CAA indicated a high specificity against C. albicans. For the Routine Laboratory we recommend screening of all yeasts with the CAA; an additional morphological examination is also recommended as cross-reactions with C.tropicalis and Torulopsis species are found. The non-agglutinating yeasts can then be further examined with the API 20 C.

A reemphasis-Germ tubes diagnostic for Candida albicans have no constrictions

Descriptive and illustrative material in several recent diagnostic manuals for medical mycology are unclear with respect to proper designation of germ tubes formed by Candida albicans. Because of the increasing significance of this and other yeast species in human disease, mycologists should be aware that germ tubes, unlike buds or pseudohyphae, do not have constrictions at the point of origin. Light and scanning electron micrographs are presented to emphasize this diagnostic characteristic.