Saccharomyces boulardii

Saccharomyces boulardii is a tropical species of yeast first isolated from lychee and mangosteen fruit in 1923 by French scientist Henri Boulard. Although early reports described distinct taxonomic, metabolic, and genetic properties, S. boulardii is a strain of S. cerevisiae, sharing >99% genomic relatedness, giving the synonym S. cerevisiae var boulardii. A type strain is Hansen CBS 5926. S. boulardii is sometimes used as a probiotic with the purpose of introducing beneficial active cultures into the large and small intestines, as well as conferring protection against pathogenic microorganisms in the host. It grows at 37 °C (98.6 °F). In addition, the popular genome-editing tool CRISPR-Cas9 was proven to be effective in S. boulardii. Boulard first isolated this yeast after he observed natives of Southeast Asia chewing on the skin of lychee and mangosteen in an attempt to control the symptoms of cholera. In healthy patients, S. boulardii has been shown to be nonpathogenic and nonsystemic (it remains in the gastrointestinal tract rather than spreading elsewhere in the body). S. boulardii was characterized as a species separate from S. cerevisiae due to some of its characteristics: it does not digest galactose and does not undergo sporulation. Its genomic sequence, however, defines it as a clade under S. cerevisiae, closest to those found in wine. Like S. cerevisiae, it has 16 chromosomes, a 2-micron circle plasmid, and is diploid with genes for both mating types, MATa and MATα. Notably, the MATa locus consistently contains some likely disabling mutations relative to spore-forming S. cerevisiae. Both S. boulardii and S. cerevisiae produce proteins that inhibit pathogenic bacteria and their toxins, specifically pho8 and ysp3. A yet-unidentified 120 kDa protein also inhibits changes in cAMP levels induced by cholera toxin. S. boulardii encodes extra copies of adhesion proteins that help to stick to pathogenic bacteria and stop them from binding to the intestinal mucus.(supp. text) Evidence exists for its use in the preventive treatment of antibiotic-associated diarrhea (AAD) in adults. Further evidence indicates its use to prevent AAD in children.The potential efficacy of probiotic AAD prevention is dependent on the probiotic strain(s) used and on the dosage. A 2015 Cochrane review recommended Lactobacillus rhamnosus or S. boulardii at 5 to 40 billion colony-forming units/day for the prevention of AAD in children, given the modest number needed to treat and the likelihood that adverse events are very rare. A recent meta-analysis of 21 randomised controlled trials (4780 participants) confirmed that S. boulardii is effective in reducing the risk of AAD in children and adults. S. boulardii showed reduction of relapses in some specific patients with recurrent Clostridium difficile infection and may be effective for secondary prevention of C. difficile infection. S. boulardii has been shown to significantly increase the recovery rate of stage IV AIDS patients suffering from diarrhea versus placebo. On average, patients receiving S. boulardii gained weight, while the placebo group lost weight over the 18-month trial. No adverse reactions were observed in these immunocompromised patients. The addition of S. boulardii to the standard triple medication protocol for elimination of Helicobacter pylori infection showed a significant increase in eradication rates in a meta-analysis, though eradication rates were still not exceptional. The supplement also significantly decreased usual side effects of H. pylori eradication therapy including diarrhea and nausea.