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Saccharomyces Cerevisiae Pathogenicity in Humans
Saccharomyces Cerevisiae is proven to be an opportunistic human pathogen, though of relatively low virulence. Despite widespread use of this microorganism at home and in industry, contact with it very rarely leads to infection. Saccharomyces Cerevisiae was found in the skin, oral cavity, oropharinx, duodenal mucosa, digestive tract and vagina of healthy humans (one review found it to be reported for 6% of samples from human intestine ). Some specialists consider S. Cerevisiae to be a part of normal microbiota of the gastrointestinal tract, the respiratory tract and the vagina while others believes that the species cannont be called a true commensal and originates in food. Presence of S. Cerevisiae in human digestive system may be rather transient, for example experiments show that in the case of oral administration to healthy individuals it is eliminated from the intestine within 5 days after the end of administration.
 * Opportunistic infection
 * Saccharomyces cerevisiae

Under certain circumstances, however, such as degraded immunity, Saccharomyces Cerevisiae can cause infection in humans. Studies show that it causes 0.45-1.06% of the cases of yeast-induced vaginitis. In some cases women suffering from S. Cerevisiae-induced vaginal infection were intimate partners of bakers, and the strain was found to be the same that their partners used for baking. As of 1999, no cases of S. Cerevisiae-induced vaginitis in women, who worked in bakeries themselves, were reported in scientific literature. Some cases were linked by researchers to the use of the yeast in home baking. Cases of infection of oral cavity and pharynx caused by S. Cerevisiae are also known.

Occasionally Saccharomyces Cerevisiae causes invasive infections (i. e. gets into the bloodstream or other normally sterile body fluid or into a deep site tissue, such as lungs, liver or spleen) that can go systemic (involve multiple organs). Such conditions are life-threatening. More than 30% cases of S. Cerevisiae invasive infections lead to death even if treated. S. Cerevisiae invasive infections, however, are much rarer than invasive infections caused by Candida albicans even in patients weakened by cancer. S. Cerevisiae causes 1% to 3.6% nosocomial cases of fungemia. A comprehensive review of S. Cerevisiae invasive infection cases found all patients to have at least one predisposing condition.

Saccharomyces Cerevisiae may enter the bloodstream or get to other deep sites of the body by translocation from oral or enteral mucosa or through contamination of intravascular catheters (e. g. central venous catheters). Intravascular catheters, antibiotic therapy and compromised immunity are major predisposing factors for S. Cerevisiae invasive infection.

A number of cases of fungemia were caused by intentional ingestion of living S. Cerevisiae cultures for dietary or therapeutic reasons, including use of Saccharomyces boulardii (a strain of S. cerevisiae which is used as a probiotic for treatment of certain forms of diarrhea). Saccharomices boulardii causes about 40% cases of invasive Saccharomyces infections and is more likely (in comparison to other S. Cerevisiae strains) to cause invasive infection in humans without general problems with immunity, though such adverse effect is very rare relative to Saccharomices boulardii therapeutic administration.

S. boulardii may contaminate intravascular catheters through hands of medical personnel involved in administering probiotic preparations of S. boulardii to patients.

Systemic infection usually occurs in patients who have their immunity compromised due to severe illness (AIDS, Leukemia, other forms of cancer) or certain medical procedures (bone marrow transplantation, abdominal surgery).

A case was reported when a nodule was surgically excised from a lung of a man embloyed in baking business, and examination of the tissue revealed presense of Saccharomyces Cerevisiae. Inhalation of dry baking yeast powder is supposed to be the source of infection in this case.

Asymptomatic colonisation
MOVED

Virulence of different strains
Not all strains of Saccharomyces Cerevisiae are equally virulent towards humans. Most enviromental strains are not capable to grow at temperatures above 35 °C (i. e. at temperatures of living body of humans and other mammalian). Virulent strains, however, are capable to grow at least above 37 °C and often up to 39 °C (rarely up to 42 °C). Some industrial strains are also capable to grow above 37 °C. European Food Safety Authority (as of 2017) requires that all S. Cerevisiae strains capable of growth above 37 °C that are added to the food or feed chain in viable form must, as to be qualified presumably safe, show no resistance to antimycotic drugs used for treatment of yeast infections.

The ability to grow at elevated temperatures is an important factor for strain's virulence but not the sole one.

Other traits that are usually believed to be associated with virulence are: ability to produce certain enzimes such as proteinase and phospholipase, invasive growth (i.e. growth with intrusion into the nutrient medium), ability to adhere to mammalian cells , ability to survive in the presence of hydrogen peroxide (that is used by macrophages to kill foreign microorganisms in the body) and other abilities allowing the yeast to resist or influence immune response of the host body. Ability to form branching chains of cells, known as pseudohiphae is also sometimes sait to be associated with virulence, though some research suggests that this trait may be common to both virulent and non-virulent strains of Saccharomyces Cerevisiae.

Literature


Healthy

Safety