Differentiation of Candida dubliniensis from Candida albicans on Staib Agar and Caffeic Acid-Ferric Citrate Agar

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Abstract
The methods currently available for the identification of the pathogenic yeast Candida dubliniensis all have disadvantages in that they are time-consuming, expensive, and/or, in some cases, unreliable. In a recent study (P. Staib and J. Morschhäuser, Mycoses 42:521–524; 1999) of 14 C. dubliniensis and 11 C. albicans isolates, it was suggested that the ability of C. dubliniensis to produce rough colonies and chlamydospores (chlamydoconidia) on Staib agar (SA) provided a simple means of differentiating it from its close relative C. albicans . In the present investigation, we examined the colony morphology and chlamydospore production of 130 C. dubliniensis and 166 C. albicans isolates on SA and on the related defined medium caffeic acid-ferric citrate agar (CAF). All of the C. dubliniensis and C. albicans isolates produced chlamydospores on the control medium, i.e., rice-agar-Tween agar. However, while none of the C. albicans isolates produced chlamydospores on either SA or CAF, 85.4 and 83.8% of the C. dubliniensis isolates produced chlamydospores on SA and CAF, respectively. All of the C. albicans isolates grew as smooth, shiny colonies on SA after 48 to 72 h of incubation at 30°C, while 97.7% of the C. dubliniensis isolates grew as rough colonies, many (65%) with a hyphal fringe. In contrast, 87.4% of the C. albicans and 93.8% of the C. dubliniensis isolates yielded rough colonies on CAF. Although the results of this study confirm that SA is a good medium for distinguishing between C. dubliniensis and C. albicans , we believe that discrimination between these two species is best achieved on the basis of colony morphology rather than chlamydospore production.