Identification of Candida dubliniensis based on temperature and utilization of xylose and alpha-methyl-D-glucoside as determined with the API 20C AUXand vitek YBC systems

To have a better understanding of the role of Candida dubliniensis in clini cal 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 alpha-me thyl-D-glucoside (MDG) and to grow poorly or not at all at 45 degrees C, wh ereas Candida albicans isolates utilize XYL and MDG and usually grow well a t 45 degrees C. We tested 66 isolates of C. dubliniensis and 100 isolates o f C. albicans with both the API 20C AUX and Vitek YBC systems to evaluate t he 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 degrees C was also examined. None of the C. dubliniensis isolates grew at 45 degrees C, and 23 of 100 C. albicans isolates (23%) exhibited poor or no growth at 45 degrees C. The XYL and MDG tests contained,within the API 20C AUX syste m 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 s ystem, 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 syste m. Clinical microbiology laboratories could use lack of growth at 45 degree s C and a negative XYL test with either the API 20C AUX or Vitek yeast iden tification system to provide a presumptive identification of C. dubliniensi s. 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.