S. boulardii

1. What conditions has S. boulardii been studied for?

• Acute infectious diarrhea (especially pediatric, including rotavirus-associated watery diarrhea) (clinical trials summarized in the diarrhea-focused review).

• Antibiotic-associated diarrhea (AAD), including prevention and reduction of incidence (multiple trials summarized; S. boulardii highlighted as one of the most effective strains).

• Clostridium difficile–associated post-antibiotic diarrhea (mentioned in the diarrhea review as an outcome where dose matters; the review notes emerging evidence).

• Helicobacter pylori infection as an adjunct to eradication therapy (double-blind placebo-controlled studies summarized in the H. pylori review).

• Inflammatory bowel disease (IBD)/colitis models, particularly DSS-induced colitis in mice, including interactions with antibiotics and other fungi (mouse study with S. boulardii CNCM I-745).

• Maternal supplementation during pregnancy/lactation to influence breast milk microbiome, infant gut microbiome, and infant health outcomes (systematic review/meta-analysis of RCTs; S. boulardii listed among strains used).

• Colon cancer/colon carcinoma (preclinical): effects of S. boulardii metabolites/cell-free extracts on human colon carcinoma cells (Caco-2) (in vitro study abstract).

• General immune modulation and broader “functional food” claims (review-level discussion of probiotics including S. boulardii, mentioning immune-modulation and cancer prevention as areas discussed broadly).

2. Does it work in treating those conditions? Summarize the evidence.

• Acute infectious diarrhea (treatment): The clinical-trial review reports that a few well-identified strains—including S. boulardii—show a statistically significant and “moderate” clinical benefit in treating acute watery diarrhea (notably rotavirus), with an average reduction in diarrhea duration of ~1 day. The review emphasizes the effect is strain-dependent and dose-dependent.

• Antibiotic-associated diarrhea (prevention): The same review states that, overall, trials “do show clear evidence of efficacy,” and identifies S. boulardii (and Lactobacillus GG) as the two most effective strains for preventing AAD. It also notes dose importance for reducing incidence.

• C. difficile–associated post-antibiotic diarrhea: The diarrhea review notes “evidence is emerging” regarding dose and incidence reduction for C. difficile–associated postantibiotic diarrhea, but does not provide effect sizes in the abstract; this suggests supportive but not definitive evidence based on the provided text.

• H. pylori (adjunctive use): The H. pylori review summarizes prospective double-blind placebo-controlled studies indicating S. boulardii can diminish bacterial load but not eradicate H. pylori on its own. It further concludes S. boulardii is a useful concomitant therapy in standard eradication protocols and “most probably increases eradication rate”, while also reducing antibiotic-associated GI adverse effects.

• IBD/colitis (animal evidence): In a DSS-colitis mouse study, S. boulardii improved DSS-induced colitis in untreated settings, but its benefit depended on the bacterial context: effects were altered by antibiotics and were restored when Enterobacteriaceae were re-established (via colistin-resistant E. coli), partly through improved fungal colonization. This supports a plausible benefit in inflammatory models but also highlights strong context-dependence and that this is preclinical.

• Maternal supplementation (microbiome/infant outcomes): A systematic review/meta-analysis of 24 RCTs concluded maternal probiotics can “effectively orchestrate” breast milk and infant gut microbiomes with “a wide range of clinical benefits and safety,” and lists S. boulardii among strains that “can be used.” However, the abstract’s quantitative result shown (a 24% risk difference for beneficial bacteria detection in breast milk) is not attributed specifically to S. boulardii, so strain-specific efficacy cannot be confirmed from the provided text.

• Colon cancer (in vitro): An in vitro study reports evaluation of S. boulardii metabolites against Caco-2 colon carcinoma cells (cytotoxicity, apoptosis, and gene-expression effects such as survivin/IL-8/NFκB). This is mechanistic/preclinical and does not establish clinical anticancer efficacy.

3. What health benefits does it have?

• Diarrhea-related benefits: Evidence summarized in clinical-trial reviews supports benefit for:

  • Prevention of antibiotic-associated diarrhea (clear evidence across trials; S. boulardii among most effective strains).

  • Treatment of acute infectious watery diarrhea with an average ~1-day reduction in duration (strain- and dose-dependent).

  • Reduction of GI adverse effects during H. pylori eradication therapy (review conclusion).

• Adjunct support in H. pylori therapy: May reduce bacterial load and increase eradication rates when used alongside standard therapy (review-level conclusion; not standalone eradication).

• Potential anti-inflammatory effects (preclinical): Improved DSS-induced colitis in mice, with effects shaped by bacteria–fungi interactions and antibiotic exposure.

• Potential immune-modulatory and broader functional-food benefits: A general probiotics/prebiotics/synbiotics review lists immune-modulation and cancer prevention among discussed benefits for these interventions (not necessarily proven specifically for S. boulardii in humans from the abstract text).

• Proposed antimicrobial mechanisms: A mechanistic abstract notes unique mutations in S. boulardii associated with high acetic acid accumulation that can inhibit bacterial growth, offering a plausible mechanism for some probiotic effects.

• Food/fermentation-related functional attributes (review-level): A dairy-focused review claims S. boulardii-containing dairy products may produce organic acids, enzymes, vitamins, and metabolites, and states it is “known to reduce serum cholesterol levels,” but these are broad claims in a review abstract without specific trial details provided here.

4. Does it have any downsides or side effects?

• Evidence limitations and context-dependence: A review of S. boulardii notes that while clinical trials indicate it can alleviate GI infection symptoms “to some extent,” further trials are needed to define full therapeutic potential—implying uncertainty and variability in outcomes.

• Effects may depend on concurrent antibiotics and microbiome state (preclinical): In DSS-colitis mice, antibiotic treatment (vancomycin vs colistin) dramatically changed susceptibility to colitis and whether S. boulardii had an effect, suggesting benefits may not be uniform across clinical contexts where antibiotics alter gut ecology.

• Potential trade-off from acetic-acid–related phenotype (mechanistic/genetic): Natural isolates with a specific mutation (whi2S270*) accumulate high acetic acid that inhibits bacterial growth, but the same mutation is also associated with acetic acid sensitivity and acid sensitivity (as stated in the abstract). This suggests a plausible “built-in” vulnerability of certain S. boulardii lineages under harsh acidic conditions, though clinical relevance is not established from the provided text.

• Safety signals in the provided abstracts: The maternal probiotic systematic review/meta-analysis concludes probiotics had “clinical benefits and safety,” but does not provide S. boulardii–specific adverse event rates in the abstract text.

5. Is it beneficial or harmful for any genetic variations (pharmacogenomics)?

The provided abstracts do not describe human pharmacogenomic interactions (i.e., patient genetic variants predicting response or risk) for S. boulardii. However, they do provide relevant information on genetic variation within the yeast itself.

• Yeast genetic variants that may influence probiotic function: One abstract reports that natural S. boulardii isolates (Sb.P and Sb.A) are homozygous for a recessive mutation whi2S270*, associated with high acetic acid accumulation and inhibition of bacterial growth (a potentially beneficial antimicrobial mechanism).

• Potential downside linked to the same yeast mutation: The same abstract notes the homozygous whi2S270* mutation also leads to acetic acid sensitivity and acid sensitivity, which could theoretically affect viability or performance under certain conditions (clinical implications not established in the abstract).

• Future direction—engineered strains: A review notes that improving probiotic function using engineered yeast is an attractive direction and that genome engineering tools for S. boulardii have been limited until recently, implying that strain genetics may become increasingly relevant to efficacy and safety, but specific pharmacogenomic guidance is not provided.

References

1. Probiotics, prebiotics and synbiotics- a review.
   Kavita R Pandey, Suresh R Naik, Babu V Vakil (2015) - Journal of food science and technology
2. Health-promoting properties ofSaccharomyces cerevisiae var. boulardiias a probiotic; characteristics, isolation, and applications in dairy products
   Fereshteh Ansari, Shohre Alian Samakkhah, Ali Bahadori, Seyedeh Maedeh Jafari, Mojtaba Ziaee (2023)
3. Yeasts as probiotics: Mechanisms, outcomes, and future potential.
   Swastik Sen, Thomas J Mansell (2020) - Fungal genetics and biology : FG & B
4. Both
   Xinge Xu, Jingwei Wu, Yuxin Jin, Kunlun Huang, Yuanyuan Zhang, Zhihong Liang (2023) - Nutrients
5. Probiotics for prevention and treatment of diarrhea.
   Stefano Guandalini (2011) - Journal of clinical gastroenterology
6. Enterobacteriaceae are essential for the modulation of colitis severity by fungi.
   Bruno Sovran, Julien Planchais, Sarah Jegou, Marjolene Straube, Bruno Lamas, Jane Mea Natividad, Allison Agus, Louise Dupraz, Jérémy Glodt, Grégory Da Costa, Marie-Laure Michel, Philippe Langella, Mathias L Richard, Harry Sokol (2018) - Microbiome
7. Effects of maternal probiotic supplementation on breast milk microbiome and infant gut microbiome and health: a systematic review and meta-analysis of randomized controlled trials.
   Bekalu Kassie Alemu, Getnet Gedefaw Azeze, Ling Wu, So Ling Lau, Chi Chiu Wang, Yao Wang (2023) - American journal of obstetrics & gynecology MFM
8. Saccharomyces boulardii alleviates DSS-induced intestinal barrier dysfunction and inflammation in humanized mice.
   Bei Li, Haibo Zhang, Linlin Shi, Rong Li, Yanan Luo, Yun Deng, Shihan Li, Ruizhen Li, Zhi Liu (2022) - Food & function
9. Reproductive Effects of
   Çiğdem Sevim, Erol Akpınar, Emrah Hicazi Aksu, Ali Doğan Ömür, Serkan Yıldırım, Mehtap Kara, İsmail Bolat, Aristides Tsatsakis, Robin Mesnage, Kirill S Golokhvast, Sevgi Karabulut Uzunçakmak, Rabia Nilüfer Ersoylu (2023) - Toxics
10. Anticancer Properties of Saccharomyces boulardii Metabolite Against Colon Cancer Cells.
    Babak Pakbin, Samaneh Allahyari, Shaghayegh Pishkhan Dibazar, Amir Peymani, Mozhdeh Khajeh Haghverdi, Khadijeh Taherkhani, Maryam Javadi, Razzagh Mahmoudi (2024) - Probiotics and antimicrobial proteins
11. In vitro digestion and characterization of selenized Saccharomyces cerevisiae, Pichia fermentans and probiotic Saccharomyces boulardii.
    Ivana Hyrslova, Antonin Kana, Vera Nesporova, Iva Mrvikova, Agapi I Doulgeraki, Barbora Lampova, Ivo Doskocil, Sarka Musilova, Marek Kieliszek, Gabriela Krausova (2024) - Journal of trace elements in medicine and biology : organ of the Society for Minerals and Trace Elements (GMS)
12. Are probiotics useful in Helicobacter pylori eradication?
    Matjaž Homan, Rok Orel (2015) - World journal of gastroenterology
13. Enhancing probiotic impact: engineeringSaccharomyces boulardiifor optimal acetic acid production and gastric passage tolerance
    Bruna Trindade de Carvalho, Ana Subotić, Paul Vandecruys, Sara Deleu, Séverine Vermeire (2024)
14. Saccharomyces boulardii CNCM I-745 supports regeneration of the intestinal microbiota after diarrheic dysbiosis - a review.
    Margret I Moré, Alexander Swidsinski (2015) - Clinical and experimental gastroenterology
15. Impact of Saccharomyces boulardii CNCM I-745 on Bacterial Overgrowth and Composition of Intestinal Microbiota in Diarrhea-Predominant Irritable Bowel Syndrome Patients: Results of a Randomized Pilot Study.
    Luis Maria Bustos Fernández, Fernando Man, Juan Sebastián Lasa (2023) - Digestive diseases (Basel, Switzerland)
16. Can the Evidence-Based Use of Probiotics (Notably Saccharomyces boulardii CNCM I-745 and Lactobacillus rhamnosus GG) Mitigate the Clinical Effects of Antibiotic-Associated Dysbiosis?
    Dan Waitzberg, Francisco Guarner, Iva Hojsak, Gianluca Ianiro, D Brent Polk, Harry Sokol (2024) - Advances in therapy
17. Effectiveness of phototherapy with and without probiotics for the treatment of indirect hyperbilirubinaemia in preterm neonates: a randomised controlled trial.
    Hisham Nasief, Meshari A Alaifan, Shadi Tamur, Khalid Khadawardi, Ammar A Bahauddin, Aijaz Ahmed, Sarfraz Ahmad, Rajinder Singh, Bakr H Alhussaini, Amber Hassan (2024) - Paediatrics and international child health
18. Saccharomyces boulardii attenuates lipopolysaccharide-induced anxiety-like behaviors in rats.
    Fatemeh Babaei, Mohammadreza Mirzababaei, Ghazaleh Mohammadi, Leila Dargahi, Marjan Nassiri-Asl (2022) - Neuroscience letters
19. Microbiome Engineering Using Probiotic Yeast:
    Jungyeon Kim, Christine Atkinson, Michael J Miller, Kyoung Heon Kim, Yong-Su Jin (2023) - Microbiology spectrum
20. Effectiveness and safety of Saccharomyces boulardii for acute infectious diarrhea.
    Ener Cagri Dinleyici, Makbule Eren, Metehan Ozen, Zeynel Abidin Yargic, Yvan Vandenplas (2012) - Expert opinion on biological therapy