Introduction

Saccharomyces cerevisiae, which in Latin means "sugar fungus," has been utilized by humans for thousands of years. It is believed that it was first discovered on the skins of grapes. S. cerevisiae is a budding or brewing yeast, and has been put to use since antiquity to make dough rise and to provide ethanol in alcoholic beverages. One of the most elemental purposes of brewers yeast was that it transformed the way bread was made in ancient times. Once, all bread was unleavened, and could often have a hard, dry texture. One can only imagine the reaction when yeast was accidentally added to the bread mixture an estimated 5,000 years ago in Egypt, yielding a chewy, flavorful diet staple. (1) Yeast remains a key component in baking to this day. The pioneering research of Louis Pasteur in the 1860s included a method of enabling yeast to be commercially produced as an ingredient for baking and in the processing of alcoholic beverages.

Its deeply detailed cellular structure makes S. cerevisiae, also known as "brewers yeast," one of the most highly researched model organisms in the study of biology. It exists in single-cell form, or in pseudomyceliac form. Cellular reproduction occurs by budding. The ability of S. cerevisiae to ferment specific sugars is a major factor that differentiates it from other yeasts.

S. cerevisiae exists and grows in the haploid and diploid cellular forms. The haploid life cycle consists of mitosis, growth, and ultimately death, the latter more rapid under extremely stressful conditions. Diploid cells also undergo mitosis as well as growth, but in the same stressful circumstances can experience sporulation. Subsequent to sporulation, the cells undergo meiosis and produce a number of haploid spores. These haploid spores progress to mate.

Benefits of S. Cerevisiae

A probiotic in terms of its beneficial effects, S. cerevisiae has many properties from the most basic to highly advanced. When ingested in a quantity of two tablespoons daily, the commercially prepared product known as "nutritional yeast" provides 52 percent of the recommended daily amount (RDA) of protein. Nutritional yeast is also high in fiber, B vitamins and folic acid. It is also gluten-free, which makes it an attractive supplement to people who are wheat-intolerant.

Nutritional yeast also has the presence of beta-1,3 glucans, which have been shown to stimulate the body's immune system. Researchers at the University of Louisville established a receptor found on the surface of certain immune cells is known for binding itself to beta-glucans, which permits the immune cells to recognize the beta-glucans as being dissimilar. (2) While some pharmaceutical drugs are capable of over-stimulating the body's immune system during therapy and are therefore not suitable for people with autoimmune illnesses, beta-glucans appear to assist the immune system without causing overactivity (3). Beta-glucans are also apparently capable of lowering LDL cholesterol levels, assisting in the healing of wounds and aid in the prevention of infections.

Beta-glucans derived from shiitake mushrooms have been applied as immunoadjuvant treatment for cancers since 1980. This therapy is particularly popular in Japan. Several studies indicate that beta-glucans can prevent the formation of tumors and the development of cancers. (4,5,6) In an experiment conducted with mice, beta 1,3 glucans administered with interferon gamma slowed the progress of tumors and metastasis to the liver. (7) It was also proved that among human colorectal cancer patients, ingestion of beta-1,3 glucans from shiitake mushrooms, along with chemotherapy, generated a longer rate of survival. (8)

Prepared yeast is also easily stored. Often vacuum-packed or sealed in individual doses, this form of S. cerevisiae is shelf-stable for approximately one year.

Safety of S. Cerevisiae

People have contact with S. cerevisiae daily, whether by way of inhalation or ingesting it as, perhaps, as health supplement This "brewers yeast" has a long track record of safety. Studies were conducted in 1961 to determine whether consuming large quantities of S. cerevisiae would produce a result of colonization of the yeast, or its transmission to other body organs. The studies showed that extremely high consumption of S. cerevisiae would result in passage and colonization to draining of the lymph nodes. However, a large feeding of approximately ten S. cerevisiae in one dose administered to laboratory rats was needed to achieve a noticeable passage to the rats' lymph nodes. This was found to be quite in excess of the S. cerevisiae encountered on a normal daily basis. (9)

While S. cerevisiae is not generally regarded as an infective agent, a few isolated incidents listed the yeast as a factor in certain infections. Studies conducted in 1984 (10) indicated S. cerevisiae as being at least partially culpable in causing infections in patients. However, all of the patients observed had underlying health problems, and some had ingested antibiotics that killed off beneficial bacteria, giving rise to the mycotic organisms.

S. cerevisiae does not produce toxins that are harmful to humans or animals. However, it is capable of producing what are known as "killer toxins" that are fatal to other yeasts. S. cerevisiae is sometimes used in food and beverage preparation facilities to control the contamination of fermentation production areas by other kinds of yeasts.

In very rare cases, S. cerevisiae causes vaginitis. According to a 1999 article in the Journal of Clinical Microbiology, a small but increasing number of isolations of S. cerevisiae were found in women of childbearing age. In a study conducted among these women, DNA typing isolated the yeast in women who had vaginitis symptoms, or who were asymptomatic. (11)

REFERENCES:

(1) "The History of Bread Yeast," British Broadcast Corporation, 2006.
(2) Vetvicka, V., Thornton B.P., Ross G.D. (1996-07-01). "Soluble Beta-Glucan Polysaccharide Bnding to the Lectin site of Neutrophil or Natural Killer Cell Complement Receptor Type 3 (CD11b/CD18) Generates a Primed State of the Receptor Capable of Mediating Cytotoxicity of iC3b-opsonized Target Cells." The Journal of Clinical Investigation (United States: American Society for Clinical Investigation) 98 (1): 50 61.
(3) Chihara, G. (1992). "Recent Progress in Immunopharmacology and Therapeutic Effects of Polysaccharides." Developments in Biological Standardization, 77: 191 197.
(4) DiLuzio, N.R.; Williams D.L., McNamee R.B., Malshet V.G. (1980). "Comparative Evaluation of the Tumor Inhibitory and Antibacterial Activity of Solubilized and Particulate Glucan." Recent Results in CancerResearch. Fortschritte der Krebsforschung. Progr s dans les Recherches sur le Cancer 75: 165 172. ISSN 0080-0015.
(5) Morikawa, K., Takeda, R., Yamazaki, M., Mizuno, D, (April 1985). "Induction of Tumoricidal Activity of Polymorphonuclear Leukocytes by a Linear Beta-1,3-D-Glucan and other Immunomodulators in Murine Cells." Cancer 45 (4): 1496 1501.
(6) Mansell, P.W., Ichinose, H., Reed, R.J., Krementz, E.T., McNamee, R., Di Luzio, N.R. (March 1975). "Macrophage-Mediated Destruction of Human Malignant Cells in Vivo." Journal of the National Cancer Institute 54 (3): 571 580.
(7) Sveinbj rnsson, B., Rushfeldt, C., Seljelid, R., Smedsr d, B. (May 1998). "Inhibition of Establishment and Growth of Mouse Liver Metastases after Treatment with Interferon Gamma and Beta-1,3-D-Glucan." Hepatology 27 (5): 1241 1248.
(8) Wakui, A., Kasai, M., Konno, K., Abe, R., Kanamaru, R., Takahashi, K., Nakai, Y., Yoshida, Y., Koie, H., Masuda, H., et al. (April 1986). "Randomized study of lentinan on patients with advanced gastric and colorectal cancer. Tohoku Lentinan Study Group" (in Japanese). Gan to kagaku ryoho. Cancer & chemotherapy (Japan: Gan To Kagaku Ryohosha) 13 (4 pt 1): 1050 1059
(9) Wolochow, H., Hildegrand, G.J,, and Lamanna, C. (1961). "Translocation of microorganisms across the intestinal wall of the rat: effect of microbial size and concentration." Journal of Infectious Diseases 116: 523-528.
(10) Eng, R., Drehmel, R., Smith, S. and Goldstein, E. (1984). "Saccharomyces Cerevisiae Infections in Man," Medical Mycology 1984, 22, No. 5: 403-407.
(11) Posteraro, B., Sanguinetti, M., D'Amore, G., Masucci, L., Morace, G. and Fadda, G. (July 1999). "Molecular and Epidemiological Characterization of Vaginal Saccharomyces Cerevisiae Isolates," Journal of Clinical Microbiology, 37 (7): 2230-2235.

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