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Saccharomyces spp.
(described by Meyen ex Hansen in 1883)

Say Me

Taxonomic Classification

Kingdom: Fungi
Phylum: Ascomycota
Class: Hemiascomycetes
Order: Saccharomycetales
Family: Saccharomycetaceae
Genus: Saccharomyces

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 [376], 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 [1146]. 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.) [1479], which is now used in treatment of intestinal disorders, such as antibiotic-associated diarrhea [1053] 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 [2010], 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 [2119]. Saccharomyces cerevisiae has also been isolated from periodontal lesions of HIV-infected patients [1107] and from oral leukoplakia [1255]. Also, vaginitis due to Saccharomyces cerevisiae has been very rarely reported [1832].

Overload during Saccharomyces boullardii therapy has also been reported to lead to fungemia, particularly in critically-ill patients [765, 1337, 1646].

Macroscopic Features

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 [531].

Microscopic Features

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 [1295].

Histopathologic Features

Budding yeast cells may be observed. See also our histopathology page.

Compare to

Saccharomyces should be differentiated from other yeasts. Multipolar budding, production of ascospores, and fermentation profile aid in identification of Saccharomyces [531].

Laboratory Precautions

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 [2010]. On the other hand, amphotericin B and flucytosine MICs appear low [178]. The novel triazole, posaconazole and the novel echinocandin, anidulafungin also appear promising [179].

For MICs of various antifungal drugs for Saccharomyces, see our susceptibility database.

Amphotericin B appears as the drug of choice in treatment of severe infections due to Saccharomyces cerevisiae [141, 681].






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179. Barchiesi, F., D. Arzeni, A. W. Fothergill, L. F. Di Francesco, F. Caselli, M. G. Rinaldi, and G. Scalise. 2000. In vitro activities of the new antifungal triazole SCH 56592 against common and emerging yeast pathogens. Antimicrob. Agents Chemother. 44:226-229.

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679. Ernst, J. F., J. J. Mermod, and L. H. Richman. 1992. Site-specific O-glycosylation of human granulocyte/macrophage colony-stimulating factor secreted by yeast and animal cells. European Journal of Biochemistry. 203:663-7.

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735. Fiore, N. F., J. H. Conway, K. W. West, and M. B. Kleiman. 1998. Saccharomyces cerevisiae infections in children. Pediat Inf Dis J. 17:1177-1179.

765. Fredenucci, I., M. Chomarat, C. Boucaud, and J. P. Flandrois. 1998. Saccharomyces boulardii fungemia in a patient receiving ultra- levure therapy. Clin Infect Dis. 27:222-223.

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1187. Khan, S. I., A. C. Nimrod, M. Mehrpooya, J. L. Nitiss, L. A. Walker, and A. M. Clark. 2002. Antifungal activity of eupolauridine and its action on DNA topoisomerases. Antimicrob. Agents Chemother. 46:1785-1792.

1222. Koike, K., M. Ogawa, J. N. Ihle, T. Miyake, T. Shimizu, A. Miyajima, T. Yokota, and K. Arai. 1987. Recombinant murine granulocyte-macrophage (GM) colony-stimulating factor supports formation of GM and multipotential blast cell colonies in culture: comparison with the effects of interleukin-3. Journal of Cellular Physiology. 131:458-64.

1225. Kontoyiannis, D. P. 2000. Efflux-mediated resistance to fluconazole could be modulated by sterol homeostasis in Saccharomyces cerevisiae. J Antimicrob Chemother. 46:199-203.

1226. Kontoyiannis, D. P. 2000. Fluconazole inhibits pseudohyphal growth in Saccharomyces cerevisiae. Chemotherapy. 46:100-3.

1227. Kontoyiannis, D. P. 1999. Genetic analysis of azole resistance by transposon mutagenesis in Saccharomyces cerevisiae. Antimicrob. Agents Chemother. 43:2731-5.

1228. Kontoyiannis, D. P. 2000. Modulation of fluconazole sensitivity by the interaction of mitochondria and erg3p in Saccharomyces cerevisiae. J Antimicrob Chemother. 46:191-7.

1231. Kontoyiannis, D. P., and S. Rupp. 2000. Cyclic AMP and fluconazole resistance in Saccharomyces cerevisiae. Antimicrob. Agents Chemother. 44:1743-4.

1232. Kontoyiannis, D. P., N. Sagar, and K. D. Hirschi. 1999. Overexpression of Erg11p by the regulatable GAL1 promoter confers fluconazole resistance in Saccharomyces cerevisiae. Antimicrob. Agents Chemother. 43:2798-2800.

1251. Krcmery, V., I. Krupova, and D. W. Denning. 1999. Invasive yeast infections other than Candida spp. in acute leukaemia. J Hosp Infect. 41:181-194.

1255. Krogh, P., P. Holmstrup, P. Vedtofte, and J. J. Pindborg. 1986. Yeast organisms associated with human oral leukoplakia. Acta Derm Venereol Suppl. 121:51-5.

1268. Kurtz, M. B., and C. M. Douglas. 1997. Lipopeptide inhibitors of fungal glucan synthase. J Med Vet Mycol. 35:79-86.

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1337. Lherm, T., C. Monet, B. Nougiere, M. Soulier, D. Larbi, C. Le Gall, D. Caen, and C. Malbrunot. 2002. Seven cases of fungemia with Saccharomyces boulardii in critically ill patients. Intens Care Med. 28:797-801.

1370. Lorenz, C., S. Strahl-Bolsinger, and J. F. Ernst. 1992. Specific in vitro O-glycosylation of human granulocyte-macrophage colony-stimulating-factor-derived peptides by O-glycosyltransferases of yeast and rat liver cells. European Journal of Biochemistry. 205:1163-7.

1390. Lupetti, A., R. Danesi, M. Campa, M. Del Tacca, and S. Kelly. 2002. Molecular basis of resistance to azole antifungals. Trends Mol Med. 8:76-81.

1409. Maesaki, S., P. Marichal, M. A. Hossain, D. Sanglard, H. V. Bossche, and S. Kohno. 1998. Synergic effects of tacrolimus and azole antifungal agents against azole-resistant Candida albicans strains. J Antimicrob Chemother. 42:747-753.

1479. McCullough, M. J., K. V. Clemons, J. H. McCusker, and D. A. Stevens. 1998. Species identification and virulence attributes of Saccharomyces boulardii (nom. inval.). J Clin Microbiol. 36:2613-2617.

1549. Miyajima, A., K. Otsu, J. Schreurs, M. W. Bond, J. S. Abrams, and K. Arai. 1986. Expression of murine and human granulocyte-macrophage colony-stimulating factors in S. cerevisiae: mutagenesis of the potential glycosylation sites. EMBO Journal. 5:1193-7.

1581. Morrison, V. A., R. J. Haake, and D. J. Weisdorf. 1993. The spectrum of non-Candida fungal infections following bone marrow transplantation. Medicine (Baltimore). 72:78-89.

1593. Muehrcke, D. D., B. W. Lytle, and D. M. Cosgrove, 3rd. 1995. Surgical and long-term antifungal therapy for fungal prosthetic valve endocarditis. Annals of Thoracic Surgery. 60:538-43.

1632. Nenoff, P., U. Oswald, and U. F. Haustein. 1999. In vitro susceptibility of yeasts for fluconazole and itraconazole. Evaluation of a microdilution test. Mycoses. 42:629-639.

1646. Niault, M., F. Thomas, J. Prost, F. H. Ansari, and P. Kalfon. 1999. Fungemia due to Saccharomyces species in a patient treated with enteral Saccharomyces boulardii. Clin Infect Dis. 28:930.

1826. Ponton, J., R. Ruchel, K. V. Clemons, D. C. Coleman, R. Grillot, J. Guarro, D. Aldebert, P. Ambroise-Thomas, J. Cano, A. J. Carrillo-Munoz, J. Gene, C. Pinel, D. A. Stevens, and D. J. Sullivan. 2000. Emerging pathogens. Med Mycol. 38:225-236.

1832. Posteraro, B., M. Sanguinetti, G. D'Amore, L. Masucci, G. Morace, and G. Fadda. 1999. Molecular and epidemiological characterization of vaginal Saccharomyces cerevisiae isolates. J Clin Microbiol. 37:2230-2235.

1968. Rose, H. D., and V. P. Kurup. 1977. Colonization of hospitalized patients with yeast-like organisms. Sabouraudia. 15:251-6.

2010. Salonen, J. H., M. D. Richardson, K. Gallacher, J. Issakainen, H. Helenius, O. P. Lehtonen, and J. Nikoskelainen. 2000. Fungal colonization of haematological patients receiving cytotoxic chemotherapy: emergence of azole-resistant Saccharomyces cerevisiae. J Hosp Infect. 45:293-301.

2119. Smith, D., D. Metzgar, C. Wills, and J. Fierer. 2002. Fatal Saccharomyces cerevisiae aortic graft infection. J Clin Microbiol. 40:2691-2692.

2202. Sutton, D. A., A. W. Fothergill, and M. G. Rinaldi (ed.). 1998. Guide to Clinically Significant Fungi, 1st ed. Williams & Wilkins, Baltimore.

2462. Xu, J. P., C. M. Boyd, E. Livingston, W. Meyer, J. F. Madden, and T. G. Mitchell. 1999. Species and genotypic diversities and similarities of pathogenic yeasts colonizing women. J Clin Microbiol. 37:3835-3843.

2496. Zhu, D. X., Z. C. Hua, X. F. Liang, X. K. Zhang, Y. Ding, J. Q. Zhu, and K. K. Han. 1993. Purification and characterization of the biologically active human truncated macrophage colony-stimulating factor expressed in Saccharomyces cerevisiae. Biological Chemistry Hoppe-Seyler. 374:903-8.

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