saccharomyces boulardii saccharomyces boulardii saccharomyces boulardii is a tropical yeast first isolated from lychee and mangosteen fruit peel in 1923 by french scientist henri boulard. although early reports claimed distinct taxonomic, metabolic, and genetic properties, s. boulardii is genetically a grouping of s. cerevisiae strains, sharing >99% genomic relatedness, giving the synonym s. cerevisiae var. boulardii. saccharomyces boulardii scientific classification kingdom: fungi division: ascomycota class: saccharomycetes order: saccharomycetales family: saccharomycetaceae genus: saccharomyces species: s. boulardii binomial name saccharomyces boulardiiseguela, bastide & massot, 1923 (nom. inval.) type strain hansen cbs 5926 synonyms s. cerevisiae var. boulardii s. boulardii is sometimes used as a probiotic with the purpose of introducing beneficial microbes into the large and small intestines and conferring protection against pathogens. 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). biology s. boulardii was characterized as a species separate from s. cerevisiae because it does not digest galactose and does not undergo sporulation. it also tolerates human body temperature, gastric acid, and digestive enzymes better. despite all these phenotypic differences, its genomic sequence defines it as a clade under s. cerevisiae, closest to those found in wine. like ordinary s. cerevisiae, it has 16 chromosomes, a 2-micron circle plasmid, and is diploid with genes for both mating types, mata and matα. however, the mata locus contains some likely disabling mutations relative to spore-forming s. cerevisiae. both s. boulardii and ordinary s. cerevisiae produce proteins that inhibit pathogenic bacteria and their toxins, specifically 63-kda phosphatase pho8 (inhibiting e. coli endotoxin) and 54-kda serine protease ysp3 (hydrolyzing c. difficile toxins a and b). a yet-unidentified 120 kda protein also inhibits changes in camp levels induced by cholera toxin. s. boulardii encodes extra copies of yeast adhesion proteins called flocculins that help to stick to pathogenic bacteria and stop them from binding to the intestinal mucus.: supp. text medical uses saccharomyces boulardiiclinical datatrade namesdiarsafe, florastoratc codea07fa02 (who) legal statuslegal status us: over-the-counter eu: rx & otc cn: rx & otc the best-characterized "type" cbs 5926 strain is also deposited as atcc 74012 and cncm i-745. a cncm i-1049 strain is also used; it is unclear whether it is the same as cbs 5926. antibiotic-associated diarrhea 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 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. lactobacillus rhamnosus or saccharomyces boulardii at high doses (more than 5 billion colony-forming units/day) is moderately effective (with no serious side effects) for the prevention of aad in children and might also reduce the duration of diarrhea. clostridium difficile infection 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. hiv/aids-associated diarrhea s. boulardii has been shown to significantly increase the recovery rate of stage iv aids patients with 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. elimination of helicobacter pylori infection