Identification of Candida dubliniensis Based on Temperature and Utilization of Xylose and α-Methyl- d -Glucoside as Determined with the API 20C AUX and Vitek YBC Systems

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Abstract
To have a better understanding of the role of Candida dubliniensis in clinical infections, it is essential that microbiology laboratories can identify this species rapidly and accurately in clinical specimens. C. dubliniensis has been reported to lack the ability to utilize xylose (XYL) and α-methyl-d-glucoside (MDG) and to grow poorly or not at all at 45°C, whereas Candida albicans isolates utilize XYL and MDG and usually grow well at 45°C. We tested 66 isolates ofC. dubliniensis and 100 isolates of C. albicanswith both the API 20C AUX and Vitek YBC systems to evaluate the ability of the XYL and MDG tests contained within each of these systems to distinguish between the two species. The ability to grow at 45°C was also examined. None of the C. dubliniensis isolates grew at 45°C, and 23 of 100 C. albicans isolates (23%) exhibited poor or no growth at 45°C. The XYL and MDG tests contained within the API 20C AUX system were both negative for all 66 C. dubliniensis isolates and were positive for 98 (XYL) and 56 (MDG) of the 100 C. albicans isolates. With the Vitek system, 64 of 66 C. dubliniensis isolates (97.0%) were XYL negative and 63 (95.0%) were MDG negative. Conversely, 96 of 100 C. albicans isolates (96.0%) were XYL positive and 100 (100.0%) were MDG positive with the Vitek system. Clinical microbiology laboratories could use lack of growth at 45°C and a negative XYL test with either the API 20C AUX or Vitek yeast identification system to provide a presumptive identification of C. dubliniensis. A negative MDG test result with either system would also be helpful but may misclassify C. albicans as C. dubliniensis, especially when the API 20C AUX system is used.