Candida dubliniensis
On Sabouraud's dextrose agar colonies are white to cream coloured, smooth, glabrous yeast-like in appearance [and are indistinguishable from those of C. albicans] . Microscopic morphology shows numerous ovoid, budding yeast-like cells or blastoconidia, 2.0-7.0 x 3.0-8.5 um in size.
However, C. dubliniensis may be distinguished from C. albicans when grown on CHROMagar Candida. On this medium, C. albicans colonies are light blue-green in colour, while those of C. dubliniensis are a much darker green colour.
India Ink Preparation: Negative - no capsules present.
Dalmau Plate Culture on Cornmeal and Tween 80 Agar: Pseudohyphae with blastoconidia and terminal vesicles (chlamydoconidia) are produced usually in abundance [similar to C. albicans].
Physiological Tests:
Germ Tube test is Positive within 3 hours [as in C. albicans].
Hydrolysis of Urea is Negative
Growth on Cycloheximide medium is Positive
Growth at 37C is Positive [However, unlike C. albicans growth at 42C is very poor or absent].
Assimilation Tests: [Note the databases supplied by commercial systems like API 20C and ID32C do not contain profiles for C. dubliniensis, so often the first hint is a germ tube positive yeast with an unusual carbohydrate assimilation profile].
Positive: Glucose, Galactose, Maltose, Sucrose, D-Mannitol, Sorbitol, 2-Keto-gluconate,
N-Acetylglucosamine, Glucosamine.
Variable: Trehalose, Palatinose
Negative: L-Arabinose, D-Xylose, D-Ribose, L-Sorbose, L-Rhamnose, Cellobiose, Lactose, Melibiose, Melezitose, Raffinose, Glycerol, Erythritol, Inositol, DL-Lactic acid, Glucuronate, DL-Lactate, Gluconate, Esculin hydrolysis.
MIC data is limited. Antifungal susceptibility testing of individual strains is recommended.
| Antifungal | MIC ug/mL | Antifungal | MIC ug/mL |
||
Range |
MIC90 |
Range |
MIC90 |
||
| Fluconazole | 0.05->64 |
1 |
Amphotericin B | 0.03-2 |
0.125 |
| Itraconazole | 0.008->8 |
0.125 |
Flucytosine | 0.03-64 |
0.125 |
| Posaconazole | 0.003-1 |
0.125 |
Caspofungin | 0.008-1 |
0.25 |
| Voriconazole | 0.008-2 |
0.016 |
Anidulafungin | <0.125-8 |
nd |
Key Features: germ tube positive, similar to C. albicans, except for absence of growth at 42C; glycerol (mostly +), methyl-a-D-glucoside (-), trehalose (-), and D-xylose (-). Initial colonies dark green colour on CHROMagar and producing rough colonies on bird seed agar. C. dubliniensis is an uncommon cause of candidemia and mucosal infection, especially in HIV patients. RG-2 organism.
Clinical significance:
Candida dubliniensis has recently been recognised from the oral cavity of HIV-infected patients and are most frequently implicated in cases of recurrent infection following antifungal drug treatment. Phenotypically, isolates are very similar to C. albicans in that isolates produce both germ-tubes and chlamydoconidia, however, they have unusual carbohydrate assimilation patterns and grow poorly or not at all at 42C.
Mycosis: Candidiasis
Further reading:
Sullivan D. et al. Widespread geographic distribution of oral Candida dubliniensis strains in human immunodificiency virus-infected individuals. J. Clin. Micro. 1997 35:960-964.
Sullivan D. and D. Coleman. Candida dubliniensis: an emerging opportunistic pathogen. Current Topics in medical Mycology. 1997; 8:15-25.
Sullivan D and D. Coleman. Minireview. Candida dubliniensis: characteristics and identification. J. Clin. Micro. 1998; 36:329-334
