Entry 28
Probiotic science page
Uses protease-mediated toxin degradation and pathogen inhibition to reduce antibiotic-associated diarrhea and support H. pylori eradication, with meta-analysis support.
Overview
Saccharomyces boulardii CNCM I-745 is the active pharmaceutical ingredient in Florastor (Biocodex, France). It is the most clinically studied probiotic yeast [1,2]. Henri Boulard originally isolated it from lychee and mangosteen fruit in Indochina in 1923. The strain is registered at the Collection Nationale de Cultures de Microorganismes (CNCM) [7]. It is a non-pathogenic, tropical yeast. It grows optimally at 37°C. It resists gastric acid, proteases, and antibiotics. This enables oral administration during antibiotic therapy [1,7]. Multiple RCTs and meta-analyses (pools results from multiple trials) support its use for antibiotic-associated diarrhea prevention, acute gastroenteritis, and H. pylori eradication adjunct therapy [1,2,3,4].
Mechanism
S. boulardii CNCM I-745 exerts antitoxin effects. It degrades Clostridium difficile toxins A and B through a 54-kDa serine protease. This prevents toxin binding to intestinal brush border receptors [1]. The yeast enhances host intestinal anti-pathogen responses. It stimulates macrophage intracellular antimicrobial activity against Salmonella Typhimurium. It does this by modulating phagosome maturation [2] (in vitro). In epithelial cells and macrophages infected with Vibrio parahaemolyticus, CNCM I-745 prevents autophagy disruption. This preserves cellular innate defense [3] (in vitro). The strain works together with the small intestinal microbiota to boost aryl hydrocarbon receptor (AhR) signaling. This is relevant to mucosal barrier integrity in celiac disease [4] (in vitro/ex vivo). S. boulardii is not inhibited by antibacterial antibiotics. This is due to its eukaryotic nature. It is uniquely suited for co-administration during antibiotic treatment [1].
Health Benefits
A systematic review and meta-analysis (pools results from multiple trials) of pediatric acute diarrhea trials in China found that S. boulardii CNCM I-745 significantly reduced stool frequency and duration of diarrhea compared to placebo or smectite [1] (systematic review/meta-analysis). A single-center RCT enrolled adults with acute viral inflammatory diarrhea. It demonstrated that CNCM I-745 reduced inflammatory markers and shortened symptom duration [4] (RCT). In H. pylori eradication, a European multi-center registry study (Hp-EuReg) enrolled over 1,500 patients. It showed that adjunct CNCM I-745 improved eradication rates and reduced therapy-related side effects [2] (observational/registry). An RCT confirmed that S. boulardii supplementation during H. pylori eradication therapy improved tolerability. It did not reduce eradication efficacy [3] (RCT). S. boulardii CNCM I-745 also modified the fecal resistome during H. pylori therapy. It reduced antibiotic resistance gene carriage [8]. For celiac disease, CNCM I-745 boosted AhR signaling together with small intestinal microbiota [4] (in vitro). Evidence quality for diarrhea prevention and treatment is high. Multiple meta-analyses support it.
Biology
Saccharomyces boulardii CNCM I-745 is a eukaryotic, unicellular yeast. It belongs to the Saccharomycetaceae family within the phylum Ascomycota [7]. It is classified as S. cerevisiae var. boulardii. Transcriptomic analysis reveals distinct promoter sequence variability and gene expression profiles compared to S. cerevisiae laboratory strains. This is particularly true for genes governing stress resistance, filamentous growth, and iron acquisition [7] (genomics/transcriptomics). Cells are ovoid (5-10 µm × 5-7 µm). They reproduce by multilateral budding. They do not form ascospores at 37°C [7]. The strain is non-pathogenic. It does not undergo dimorphic transition. S. boulardii grows optimally at 37°C. This differs from most S. cerevisiae strains, which prefer 30°C. It tolerates low pH (2.0-3.0). It resists antibacterial antibiotics, bile salts, and pancreatic enzymes [7]. Natural isolation was from tropical fruit skins [7].
Bibliography
McFarland LV, Li T. (2025). Efficacy and safety of Saccharomyces boulardii CNCM I-745 for the treatment of pediatric acute diarrhea in China: a systematic review and meta-analysis. Frontiers in Cellular and Infection Microbiology. 15:1587792. PMID: 40535538
Nyssen OP, Jonaitis L, Pérez-Aísa Á, et al. (2026). Real-world effectiveness and safety of Saccharomyces boulardii CNCM I-745 as adjunct therapy for Helicobacter pylori eradication: data from the European Registry on H. pylori Management (Hp-EuReg). Helicobacter. 31(2):e70119. PMID: 41923280
Sjomina O, Poļaka I, Suhorukova J, et al. (2024). Randomised clinical trial: efficacy and safety of H. pylori eradication treatment with and without Saccharomyces boulardii supplementation. European Journal of Cancer Prevention. 33(3):217-222. PMID: 37942999
Salazar-Parra MA, Cruz-Neri RU, Trujillo-Trujillo XA, et al. (2023). Effectiveness of Saccharomyces boulardii CNCM I-745 probiotic in acute inflammatory viral diarrhoea in adults: results from a single-centre randomized trial. BMC Gastroenterology. 23(1):229. PMID: 37400812
Kan KR, Constante M, Rahmani S, et al. (2026). Saccharomyces boulardii CNCM I-745 synergizes with the small intestinal microbiota to boost AhR signaling in celiac disease. Gut Microbes. 18(1):2664640. PMID: 42068034
Pontier-Bres R, Czerucka D. (2026). Saccharomyces boulardii CNCM I-745 stimulates intracellular antimicrobial activity against Salmonella Typhimurium in murine macrophages. Microorganisms. 14(4):787. PMID: 42075185
Pais P, Oliveira J, Almeida V, et al. (2021). Transcriptome-wide differences between Saccharomyces cerevisiae and Saccharomyces cerevisiae var. boulardii: clues on host survival and probiotic activity based on promoter sequence variability. Genomics. 113(2):530-539. PMID: 33482324
Cifuentes SG, Prado MB, Fornasini M, et al. (2022). “Saccharomyces boulardii CNCM I-745 supplementation modifies the fecal resistome during Helicobacter pylori eradication therapy.” Helicobacter. 27(2):e12875. PMID: 34990038
Available Products
Florastor (Biocodex, Gentilly, France) is the primary commercial product containing S. boulardii CNCM I-745. It is available as capsules and sachets (250 mg, approximately 5 × 10^9 CFU (colony-forming units, a live bacteria count) per dose) [1,2]. The strain is also marketed under various brand names globally. These include Ultralevura, Perenterol, and Reflor. All use CNCM I-745 as the active ingredient. Biocodex holds the original CNCM I-745 deposit. It supplies pharmaceutical-grade material [2].