DESCRIPTIONS OF MEDICAL FUNGI
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Descriptions of Medical Fungi 71<br />
Cryptococcus neoformans (Sanfelice) Vuillemin<br />
Synonymy: Filobasidiella neoformans Kwon-Chung.<br />
Cryptococcus neoformans var. neoformans (San Felice) Vuill.<br />
RG-2 organism.<br />
This species comprises two varieties: C. neoformans var. grubii (serotype A) and C.<br />
neoformans var. neoformans (serotype D).<br />
C. neoformans var. grubii has a worldwide distribution, causing 95% of all C. neoformans<br />
infections. It has been isolated from various sources in nature and is noted for its<br />
association with accumulations of avian guano, especially with pigeon excreta. The<br />
fungus has also been isolated from the dung of caged birds including canaries, parrots<br />
and budgerigars. Other environmental isolations of C. neoformans var. grubii include<br />
rotting vegetables, fruits and fruit juices, wood, dairy products and soil.<br />
C. neoformans var. neoformans has a more restricted distribution with infections being<br />
more prevalent in Europe, including France, Italy and Denmark, where it accounts<br />
for 30% of isolates. Moreover, C. neoformans var. neoformans infections are more<br />
strongly correlated with older patients, the skin, and the use of corticosteroids (Franzot<br />
et al. 1999).<br />
Culture: Colonies (SDA) cream-coloured smooth, mucoid, yeast-like colonies.<br />
Microscopy: Globose to ovoid budding yeast-like cells 3.0-7.0 x 3.3-7.9 µm.<br />
India Ink Preparation: Positive - distinct, wide gelatinous capsules are present on<br />
direct microscopy. Some strains may not produce apparent capsules from culture.<br />
Dalmau Plate Culture: Budding yeast cells only. No pseudohyphae present.<br />
Bird Seed Agar: Colonies turn dark brown in colour as colonies selectively absorb a<br />
brown pigment from this media (Staib, 1987).<br />
Canavanine Glycine Bromothymol Blue (CGB) Agar: No growth or colour change.<br />
Creatinine Dextrose Bromothymol Blue Thymine (CDBT) Agar may be used<br />
to differentiate C. neoformans var. neoformans and C. neoformans var. grubii. C.<br />
neoformans var. neoformans grows as bright red colonies, turning the medium a bright<br />
orange after 5 days while no colour change is observed for C. neoformans var. grubii<br />
(Irokanulo et al. 1994).
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