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Laboratory Methods

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Saccharomyces cerevisiae

On Sabouraud's dextrose agar colonies are white to cream colored, smooth, glabrous and yeast-like in appearance. Microscopic morphology shows large, globose to ellipsoidal budding yeast-like cells or blastoconidia, 3.0-10.0 x 4.5-21.0 um in size.

India Ink Preparation: No capsules present.

Dalmau Plate Culture on Cornmeal And Tween 80 Agar: Usually budding blastoconidia only, however, pseudohyphae may be formed.

Physiological Tests:

Germ Tube test is Negative
Hydrolysis of Urea is Negative
Growth on Cycloheximide medium is Negative
Growth at 37C in Variable

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

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

Assimilation Tests:

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

Clinical significance:

Saccharomyces cerevisiae, commonly known as Baker's yeast, is a common environmental fungus and transient component of the normal flora of the gastrointestinal tract and skin. It has been reported from several cases of fungemia, endocarditis, and peritonitis in patients undergoing peritoneal dialysis. Disseminated infections have also been reported in both cancer patients undergoing chemotherapy and patients with AIDS.

Mycosis: Miscellaneous Yeast Infections

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.

Fungal Descriptions > Yeasts > Saccharomyces

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