Identification of Candida glabrata by a 30-Second Trehalase Test

Abstract

Rapid (30-s) trehalase tests done with material from colonies of 482 yeasts suspended in a drop of trehalose solution on a commercially supplied glucose test strip were positive for 225 (99.1%) of 227 Candida glabrata isolates grown on either of two differential media, Candida ID medium or CandiSelect medium. The test was positive for only 3 (1.2%) and 12 (4.7%) of 255 isolates of other medically important yeast species grown on the same two media, respectively. A rapid maltase test done with a subset of 255 yeast isolates was negative for all but 1 of 64 trehalase-positive C. glabrata isolates, raising the specificity of the rapid testing for C. glabrata to 98.4 to 100%, depending on the isolation medium used. Rapid trehalase and maltase tests done independently in two laboratories with 217 yeast isolates showed sensitivities of 96.0 to 98.0% and specificities of 98.2 to 99.4% for identification of C. glabrata from colonies grown on Candida ID medium. The specificity was much lower because of frequent false-positive trehalose test results when the source of colonies was Sabouraud agar formulated with 4% glucose. We conclude that direct recognition of C. albicans as blue colonies on Candida ID isolation medium coupled with the performance of the 30-s trehalase and maltase tests for C. glabrata among the white colonies on this medium will allow the rapid presumptive identification of the two yeast species most commonly encountered in clinical samples.While Candida albicans remains the principal cause of opportunistic Candida infections in immunocompromised patients, other species such as Candida glabrata, Candida krusei, Candida parapsilosis, and Candida tropicalis are also implicated. C. glabrata is now the second most common yeast species isolated from clinical specimens, constituting up to 26% of yeasts isolated from blood cultures (1,3,5,14,(20)(21)(22)(23)(24). To facilitate the yeast identification process for clinical laboratories, several chromogenic isolation media have been introduced that allow immediate identification of C. albicans (2, 8, 13, 18, 19, 25) or C. albicans, C. tropicalis, and C. krusei (7, 15) by the colors of their colonies. However, no chromogenic medium allows the specific identification of C. glabrata.C. glabrata rapidly metabolizes trehalose to glucose by means of a potent trehalase enzyme, a property shared by relatively few other yeasts of clinical importance. Stockman and Roberts (L. Stockman and G. Roberts, Abstr. 85th Annu. Meet. Am. Soc. Microbiol. 1985, abstr. 377, 1985 devised a 1-h screening test for C. glabrata based on its trehalase activity, but many isolates of C. tropicalis and several other Candida species gave false-positive results under the conditions used for that test. Various subsequent attempts to improve on the sensitivities and specificities of trehalose utilization tests for identification of C. glabrata have been described, but they necessitate preparation of heavy inoculum suspensions (suspensions of 2 to 4 on the McFarland turbidity scale) and incubati...

Comparison of VITEK 2 with ITS2-Fragment Length Polymorphism Analysis for Identification of Yeast Species

“…Discrepancies between VITEK 2, ITS-FLP, and the reference method were analyzed by repeated testing of the discrepant method and by additional tests (pigmentation of colonies on CHROMagar Candida [Chromagar Microbiologie, Paris, France] and morphology on Cornmeal-Tween 80 agar [OX-OID, Hampshire, United Kingdom]) (11). Rapid trehalose and maltose tests were used as additional tests for the identification of C. glabrata (5,6).…”

Routine Use of a Commercial Test, GLABRATA RTT, for Rapid Identification of Candida glabrata in Six Laboratories

“…Uninterpretable results had previously been explained by the carryover of glucose-containing agar in the yeast suspension (7). However, laboratories C and F, both using Sabouraud-chloramphenicol agar with 4% dextrose, obtained rates of uninterpretable results of 0.9 and 22.4%, respectively.…”

“…It is based on the ability of C. glabrata to hydrolyze trehalose and includes both a maltose test and a control test to improve the specificity of the test as previously recommended (7,15). In a preliminary study with 330 stock isolates, GLABRATA RTT reliably identified C. glabrata subcultured on three commonly used chromogenic media: Candida ID, CandiSelect, and CHROMagar Candida (8).…”

Multicenter Evaluation of a Candida albicans Peptide Nucleic Acid Fluorescent In Situ Hybridization Probe for Characterization of Yeast Isolates from Blood Cultures

“…A variety of tests have been developed for the rapid characterization of yeast isolates. These include the rapid assimilation of trehalose by Candida glabrata, the detection of rapid urease production or the detection of phenoloxidase by the caffeic acid disk test for Cryptococcus neoformans, and the germ tube test or the detection of a colonial fringe on primary isolation media for the identification of C. albicans (2,(4)(5)(6)20). A subculture onto specialized CHROMagar is another means of differentiating yeasts (19,22).…”