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Mould Identification: A Virtual Self Assessment

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Unknown 44 = Cryptococcus gattii

Case History
A 69-year-old female presented with pulmonary lesions in the right upper lobe of her lung.  Biopsy revealed the presence of encapsulated yeast-like cells and the culture shown below was isolated.
Chest X-ray

X-ray showing pulmonary cryptococcal infection [right upper lobe].
Histopathology

Tissue section stained by haematoxylin and eosin (H&E) showing numerous encapsulated yeast cells.
Culture
Culture

C. gattii on Sabouraud's dextrose agar showing typical dark cream coloured, smooth, moist, shining and mucoid colonies.
Microscopy

Microscopic morphology of C. gattii showing encapsulated budding, yeast cells. No pseudohyphae are produced.
Growth on CGB media

Canavanine-glycine-bromthymol blue (CGB) agar is now the medium of choice to determine the species status between C. gattii and C. neoformans isolates. This simple biotype test is based on the ability of C. gattii isolates to grow in the presence of L-canavanine and to assimilate glycine as a sole carbon source.
Sugar Assimilation Results
Assimilation Tests: + Positive, - Negative, V Variable,
Glucose
+
L-Rhamnose
+
Galactose
+
D-Glucosamine
v
L-Sorbose
v
N-A-D-glucosamine
v
Sucrose
+
Glycerol
-
Maltose
+
Erythritol
-
Cellobiose
+,w
Ribitol
v
Trehalose
+
Galactitol
+
Lactose
-
D-Mannitol
+
Melibiose
-
D-Glucitol
+
Raffinose
+,w
∝-M-D-glucoside
+
Melezitose
v
D-Gluconate
+
Soluble Starch
+
DL-Lactate
-
D-Xylose
+
myo-Inositol
+
L-Arabinose
+,w
Nitrate
-
D-Arabinose
+
2-K-D-gluconate
+
D-Ribose
v
D-Glucuronate
+

Urease +, Growth on 0.1% cycloheximide -, growth at 37C +

Key Features:  Encapsulated yeast; absence of pseudohyphae; growth at 37C; positive hydrolysis of urea; negative fermentation of sugars and positive assimilation of glucose, maltose, sucrose, galactose, trehalose, raffinose, inositol, cellobiose, rhamnose, arabinose, melezitose and xylose, and negative assimilation of nitrate, lactose, melibiose, erythritol and soluble starch; growth on bird seed (Guizotia abyssinica seed) or caffeic acid agar - colonies turn a dark brown colour; growth on CGB agar turning it blue within 2-5 days. RG-2 organism, however mating experiments for the production of basidiospores should be done in an appropriate pathogen handling cabinet.

About Cryptococcus Back to Virtual Assessment

What is your identification?

Cryptococcus gattii

Cryptococcus laurentii
Cryptococcus neoformans

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School of Biological Sciences
Address

THE UNIVERSITY OF ADELAIDE
SA 5005 AUSTRALIA

Contact

Dr David Ellis
Email