Cryptococcus laurentii

On Sabouraud's dextrose agar colonies are cream colored, often becoming a deeper orange-yellow with age, with a smooth mucoid texture. Microscopic morphology : Spherical and elongated budding yeast-like cells or blastoconidia, 2.0-5.5 x 3.0-7.0 um in size. No pseudohyphae present.

India Ink Preparation: Positive - narrow but distinct capsules surrounding the yeast cells are present.

Dalmau Plate Culture on Cornmeal and Tween 80 Agar: Budding yeast cells only. No pseudohyphae present.

Physiological Tests:

Germ Tube test is Negative
Hydrolysis of Urea is Positive
Growth on Cycloheximide medium is Variable
Growth at 37C is Negative (weak growth in some strains)

Fermentation Reactions: Where fermentation means the production of gas and is independent of pH changes.

Negative: Glucose; Sucrose; Lactose; Galactose; Maltose; Trehalose.

Assimilation Tests:

Positive: Glucose; Glucose; Galactose; Maltose; Sucrose; Trehalose; D-Xylose (weak); Melezitose; Lactose; Raffinose; Cellobiose; Melibiose; Inositol (delayed); L-Rhamnose; D-Arabinose; L-Arabinose; D-Mannitol; Ribitol; D-Ribose (delayed); Galactitol; Salicin.
Variable: Erythritol; Soluble Starch; D-Glucitol; Glycerol; Citric acid; DL-Lactic acid; Succinic acid.
Negative: Potassium nitrate; L-Sorbose (some positive).

Clinical significance:

Cryptococcus laurentii has been reported as a rare cause of pulmonary and cutaneous infection and CAPD associated peritonitis in humans. It may also be occasionally recovered as a saprophyte from skin.

Mycosis: Cryptococcosis

Further reading:

Kreger-Van Rij, N.J.W. (ed) 1984. The Yeasts: a taxonomic study. 3rd Edition. Elsevier Science Publishers B.V., Amsterdam, The Netherlands.

Rippon, J.W. 1988. Medical Mycology. 3rd Edition. W.B. Saunders Co., Philadelphia, USA.