Casein Agar: a Useful Medium for Differentiating Candida dubliniensis from Candida albicans

Abstract

Production of chlamydospores on casein agar at 24°C for 48 h provides a simple means for differentiating Candida dubliniensis from Candida albicans based on chlamydospore production. Of 109 C. dubliniensis isolates tested on this medium, 106 (97.2%) produced abundant chlamydospores and three produced few chlamydospores. In contrast, of the 120 C. albicans isolates tested, 111 (92.5%) failed to produce any chlamydospores, whereas the remaining nine isolates produced few chlamydospores. These findings indicate that abundant chlamydospore production on casein agar is a useful test for discriminating between C. dubliniensis and C. albicans.Since its first description in 1995, Candida dubliniensis has been isolated from a variety of specimens from humans in countries all over the world (6,13,15,(18)(19)(20). As a consequence of the increasing number of reports on the isolation of C. dubliniensis, it is important to be able to rapidly and accurately identify this species in most clinical mycology laboratories. However, identification of C. dubliniensis is hampered by its close relationship with Candida albicans, a situation that has sometimes led to the misidentification of isolates of C. dubliniensis as C. albicans (19). At present, the most accurate differentiation between isolates of the two species is performed in reference laboratories with the use of molecule-based techniques such as PCR or DNA fingerprinting with repetitive sequence-containing DNA probes (5,17,19). However, these sophisticated techniques are not suitable and often not readily applicable for use in small clinical mycology laboratories, where simple and rapid methods are needed. Reliable phenotypic methods for the identification of C. dubliniensis isolates include carbohydrate assimilation profile analysis by using commercially available yeast identification systems and detection of differential antigen expression by immunofluorescence microscopy (2,3,11,12,20). Furthermore, a variety of other ancillary tests have been developed for discriminating between C. dubliniensis and C. albicans isolates, including the inability of C. dubliniensis to grow at 45°C (12). However, whereas these tests are useful for the presumptive identification of C. dubliniensis, they are not definitive. One of the key features employed in the initial description of C. dubliniensis was its ability to produce abundant chlamydospores on cornmeal agar and rice-agar-Tween-agar (20). Chlamydospore production by C. dubliniensis on Staib agar and caffeic acid-ferric citrate agar has also been used recently for the differentiation of C. dubliniensis from C. albicans (1,17). In the present study, the production of chlamydospores by C. dubliniensis and C. albicans on casein agar was investigated as an additional means for differentiating the two species.The reference and clinical isolates used in this study are shown in Table 1. Conventional morphological and physiologic methods, as well as molecular techniques, were employed to confirm the identity of all isolates (1,2,4,5,11,19). ...

Development and Evaluation of a Rapid Latex Agglutination Test Using a Monoclonal Antibody To Identify Candida dubliniensis Colonies

“…(v) Fourier transform infrared spectroscopy analysis of all cell components present in a cell can phenotypically discriminate these two species (31). More recently, it was reported that the two species could be distinguished by culture on Staib agar, Pal's agar, modified Pal's agar, and casein agar, on which only C. dubliniensis produces abundant chlamydospores and rough colonies (1,2,3,24,28). We also described an immunochromatographic assay differentiating between C. albicans and C. dubliniensis, but C. dubliniensis was identified only by default, owing to the specificity of the monoclonal antibodies (MAbs) (19).…”

Occurrence of Candida Species Colonization in a Population of Denture-Wearing Immigrants

“…DRS has been reported in more than 60% of denture wearers, and although it is typically asymptomatic, it occasionally associates with leukoplakia, pseudomembrane formation, erythema and angular cheilitis (4,6,7).…”

“…Candida dubliniensis has recently been isolated fromthe oral cavity ofhuman immunodeficiencyvirus (HIV)-infected patients, leading to its consideration as a novel, emerging, opportunistic pathogen (4). Candida colonization and biofilm formation on dentures may depend on oral hygiene practices, such as overnight denture removal, denture cleanser use, smoking and specific denture characteristics (5).…”

Supplementation of CHROMagar Candida Medium with Pal's Medium for Rapid Identification of Candida dubliniensis

“…The remaining 131 yeast strains were clinical isolates of oral, vaginal, sputum, or blood origin previously isolated at our laboratory and included 95 C. dubliniensis strains, 29 C. albicans strains, 2 C. krusei strains, 2 C. glabrata strains, 2 C. guilliermondii strains, and 1 C. parapsilosis strain. Clinical isolates were identified by their carbohydrate assimilation patterns on ID 32C strips (bioMérieux, Marcy-l'Etoile, France), growth at 42 to 45°C, chlamydospore production in casein agar (7), and indirect immunofluorescence with a specific anti-C. dubliniensis serum (2). Genotypic identification of C. dubliniensis and C. albicans isolates was performed by PCR with specific primers.…”