(described by Meyen ex Hansen in 1883)
Description and Natural Habitats
Saccharomyces is a yeast commonly isolated from human, mammals, birds, wine, beer, fruits, trees, plants, olives, and soil. Also known as the “baker’s” or “brewer’s” yeast, Saccharomyces cerevisiae is used in food industry in production of various food stuffs, wines, and beers.
Saccharomyces cerevisiae is a genetically tractable yeast which is closely related to Candida albicans. As a consequence, Saccharomyces cerevisiae is a commonly used model yeast in fungal molecular research, including DNA sequence analysis , mechanism of action of [166, 373, 611, 1187, 1226, 1268] and resistance to [836, 1225, 1227, 1228, 1231, 1232, 1390, 1409] antifungal drugs, and the investigation of factors of pathogenicity, such as adhesion . Of note, Saccharomyces cerevisiae has also been used to express human granulocyte/macrophage colony-stimulating factor (hGM-CSF) [679, 1222, 1370, 1549, 2496]. While it is a common colonizer of mucosal surfaces [1968, 2462] and considered to be nonpathogenic for immunocompetent hosts, Saccharomyces may cause infections particularly in immunocompromised patients.
The genus Saccharomyces includes several species, the most well-known one being Saccharomyces cerevisiae. Saccharomyces boullardii (nom. inval.) , which is now used in treatment of intestinal disorders, such as antibiotic-associated diarrhea  is considered to be a synonym for a particular strain of Saccharomyces cerevisiae.
See the summary of synonyms and obselete names for the Saccharomyces spp.
Pathogenicity and Clinical Significance
Digestive colonization following ingestion of a Saccharomyces strain with diet is commonly observed. Saccharomyces spp. are now among the emerging causative agents of opportunistic mycoses in patients who are immunocompromised due to various reasons [62, 614, 1251, 1581, 1826]. Severe immunosuppression, prolonged hospitalization , prior antibiotic therapy, and prosthetic cardiac valves are the major risk factors for developing infections due to Saccharomyces. Pneumonia, endocarditis, liver abscess, fungemia, and sepsis due to Saccharomyces cerevisiae have so far been reported [141, 681, 735, 1172, 1593]. Noteworhty, fungemia and aortic graft infection has been observed in an immunocompetent host as well . Saccharomyces cerevisiae has also been isolated from periodontal lesions of HIV-infected patients  and from oral leukoplakia . Also, vaginitis due to Saccharomyces cerevisiae has been very rarely reported .
Overload during Saccharomyces boullardii therapy has also been reported to lead to fungemia, particularly in critically-ill patients [765, 1337, 1646].
Colonies of Saccharomyces grow rapidly and mature in 3 days. They are flat, smooth, moist, glistening or dull, and cream to tannish cream in color [1295, 2202].
The inability to utilize nitrate and ability to ferment various carbohydrates are typical characteristics of Saccharomyces .
Blastoconidia are observed. They are unicellular, globose, and ellipsoid to elongate in shape. Multilateral (multipolar) budding is typical. Pseudohyphae, if present, are rudimentary. Hyphae are absent [1295, 2202].
Saccharomyces produces ascospores when grown on V-8 medium, acetate ascospor agar, or Gorodkowa medium. These ascospores are globose and located in asci. Each ascus contains 1-4 ascospores. Asci do not rupture at maturity. Ascospores are stained with Kinyoun stain and ascospore stain. When stained with Gram stain, ascospores are gram-negative while vegetative cells are gram-positive .
Budding yeast cells may be observed. See also our histopathology page.
Saccharomyces should be differentiated from other yeasts. Multipolar budding, production of ascospores, and fermentation profile aid in identification of Saccharomyces .
No special precautions other than general laboratory precautions are required.
Available data suggest that MICs of fluconazole and itraconazole for Saccharomyces cerevisiae are variable [178, 1632]. Fluconazole- and itraconazole-resistant Saccharomyces cerevisiae strains have been identified . On the other hand, amphotericin B and flucytosine MICs appear low . The novel triazole, posaconazole and the novel echinocandin, anidulafungin also appear promising .
For MICs of various antifungal drugs for Saccharomyces, see our N/A(L):susceptibility database.
Amphotericin B appears as the drug of choice in treatment of severe infections due to Saccharomyces cerevisiae [141, 681].