The RapID Yeast Plus system (Innovative Diagnostic Systems, Norcross, Ga.) is a qualitative micromethod employing conventional tests and single-substrate chromogenic tests and having a 4-h incubation period. This system was compared with the API20C (bioMerieux Vitek, Hazelwood, Mo.) system, a 24- to 72-h carbohydrate assimilation method. One hundred thirty-three clinical yeast isolates, including 57 of Candida albicans, 26 of Candida tropicalis, 23 of Candida glabrata, and 27 of other yeasts, were tested by both methods. When discrepancies occurred, isolates were further tested by the Automated Yeast Biochemical Card (bioMerieux Vitek). Germ tube production and microscopic morphology were used as needed to definitively identify yeast isolates. The RapID Yeast Plus system correctly identified 125 yeast isolates, with an overall accuracy of 94% (125 of 133). Excellent correlation was found in the recognition of the three yeasts most commonly isolated from human sources. The test was 99% (105 of 106 isolates) accurate with C. albicans,C. tropicalis, and C. glabrata. The RapID Yeast Plus system compares favorably with the API20C system and provides a simple, accurate alternative to conventional assimilation methods for the rapid identification of the most commonly encountered isolates ofCandida species.
The observation of germ tube production as a method for the presumptive identification of Candida albicans has been in use for many years. Methods have recently been developed for detecting the production of the enzymes L-proline aminopeptidase and -galactosaminidase by yeast isolates grown in culture. Both enzymes are produced by C. albicans; other yeasts may produce either L-proline aminopeptidase or -galactosaminidase but not both enzymes. One hundred thirty-three clinical yeast isolates, including 55 C. albicans, 27 Candida tropicalis, 22 Torulopsis (Candida) glabrata, and 29 other yeast isolates were tested by the germ tube production method and three tests for enzyme production, with the API 20C method used as a "gold standard." All three enzymatic methods evaluated provided more objective and rapid nonmicroscopic alternatives to the germ tube test and may be used to accurately distinguish C. albicans from other yeasts.
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