Comparing Identification Methods of Candida albicans and Candida dubliniensis

Objectives: Candida albicans and Candida dubliniensis are opportunistic yeasts that are causative agents in oropharyngeal candidiasis (OPC) and are phenotypically similar, but genetically distinct.  Importance lies in the distinction between C. albicans, C. dubliniensis, and other species of Candida as causative agents of OPC, because this may affect treatment decisions. CHROMagar Candida is a proprietary medium that is commonly used by clinical laboratories and distinguishes Candida species based on colony color where C. albicans and C. dubliniensis colonies typically exhibit green hues. We sought to compare identification of C. albicans and C. dubliniensis on the basis of CHROMagar color to the gold standard - advanced PCR techniques.

Methods: 89 Candida isolates that presented with atypical colors on CHROMagar – ranging from olive and dark-green through blue-green – were subjected to molecular identification against RT-PCR using C. albicans and C. dubliniensis probes. These isolates were obtained from HIV-infected patients with a CD4+ count less than 200 or active OPC. All isolates and controls were grown on CHROMagar Candida for growth color assessment. DNA was extracted from all isolates using PrepMan® Ultra Sample Preparation Kit and subjected to RT-PCR testing using Applied Biosystems 7300 Real-Time PCR System.

Results: Microbiological testing methods identified dark green (62/89, 70%), olive (7/89, 8%), and blue-green (20/89, 22%) Candida colonies. Molecular testing methods identified C. albicans (54/89, 61%) and C. dubliniensis (24/89, 27%). 11/89 (12%) were not identified and thus were neither species.  

Conclusions: Caution is urged against using growth on CHROMagar Candida media as the sole means of species identification, as color results can be misleading since green colonies may represent species other than C. albicans and C. dubliniensis. Definitive species identification requires additional microbiological techniques or molecular techniques such as RT-PCR.