Saccharomyces boulardii CNCM I-745 restores the functionality of the gut microbiome after antibiotic stress

The educational content in this article, developed in collaboration with the Biocodex Microbiota Institute, was independently developed and approved by the GMFH publishing team and editorial staff.

Uncovering functional resilience in the gut microbiome

Antibiotic therapy, while essential in modern medicine, remains one of the most powerful disruptors of the human intestinal ecosystem. In addition to depleting microbial diversity, antibiotics also dismantle the complex metabolic network that maintains intestinal homeostasis. Restoring these functions – rather than simply recolonizing bacteria – has emerged as a central challenge in microbiome therapy¹.

Huang’s recent research et al. (2025, Intestinal microbes)² for the first time it appears that the probiotic yeast Saccharomyces boulardii CNCM I-745 not only stabilizes the composition of the intestinal microbiota during antibiotic exposure, but also restores its metabolic activity, ensuring the biochemical dialogue between microbes and host.

Using a combination of advanced in vitro gut models, metagenomics, metabolomics and human immunoassays, the authors dissected the direct effects of the yeast on the microbiota, independent of the host. This broad and successful strategy can now be used as a model for addressing functionally restorative probiotics.

From taxonomy to function: a shift in microbiome research

Traditional probiotic studies have focused on microbiota composition, examining how specific taxa increase or decrease under treatment. However, the true measure of a healthy gut ecosystem lies in function: the ability of microbes to ferment nutritional substrates, synthesize beneficial metabolites, and regulate immune balance.

Huang et al. applied quantitative microbiota profiling and shotgun metagenomics to capture both the compositional and functional dynamics of the microbiome under antibiotic pressure. In two in vitro human gut microbiota culture models, MiPro (static) and SHIME® (dynamic), the team found that amoxicillin/clavulanic acid (AMC), commonly used antibiotics in human medicine, significantly reduced bacterial biomass, diversity and metabolic output. Supplement with S. boulardii CNCM I-745 attenuated these effects, maintained bacterial loads, and restored key metabolic pathways associated with energy and carbohydrate metabolism.

This finding is critical: it shows that maintaining microbial biomass, rather than reshaping community composition, is sufficient to maintain the functional integrity of the ecosystem. The yeast acted as a stabilizing force, allowing the resident microbes to continue doing their work under antibiotic stress.

Restoring metabolic communication: propionate and indole-3-propionic acid

A highlight of the study lies in the detailed metabolomic analysis. Antibiotic exposure disrupted the production of short-chain fatty acids (SCFAs) and tryptophan-derived metabolites, molecules central to the communication between host and microbiota.

Saccharomyces boulardii Supplementation with CNCM I-745 restored the production of propionate and indole-3-propionic acid (IPA), two metabolites with different but complementary roles. Propionate, a SCFA mainly produced by Bacteroids species, modulates mucosal immunity and promotes the development of regulatory T cells. IPA, derived from tryptophan metabolism, strengthens the integrity of the epithelial barrier and dampens NF-κB-mediated inflammation.

Interestingly enough, S. boulardii itself showed minimal intrinsic metabolic activity under anaerobic conditions, suggesting that the observed effects arise from ecological facilitation; the yeast supports the recovery and activity of native bacteria rather than acting as a direct metabolic producer. This subtle yet powerful mechanism may represent a defining characteristic of probiotic yeasts.

Reduction of the pro-inflammatory potential of antibiotic-disrupted microbiota

To investigate host relevance, the authors exposed human immune cells (PBMCs) and intestinal mucosal explants from healthy subjects to microbiota-derived supernatants from the MiPro and/or the SHIME^® model. Microbiota exposed to antibiotics alone induced strong pro-inflammatory cytokine secretion, including TNF-α, IL-6 and MCP-1. In contrast, exposure to S. boulardii-supplemented microbiota significantly reduced these inflammatory signals. Note, S. boulardii the supernatant itself showed minimal effects on cytokine production by human cells.

These findings suggest that S. boulardii exerts indirect immunomodulatory effects mediated by the restored metabolic activity of the microbiome. By maintaining production of anti-inflammatory metabolites such as SCFAs and IPA, the yeast contributes to an environment conducive to immune tolerance and mucosal repair.

This mechanistic clarity strengthens the rationale for investigating microbial metabolites, driven therapies to complement antibiotics and increases our understanding of the microbiota-metabolite-immune axis in gut resilience.

Scientific and methodological progress

One of the most valuable contributions of this study lies in its methodological rigor. By static (MiPro) and dynamic (SHIME^®) in vitro systems with immunoassays on human cells, the team demonstrated how S. boulardiiThe effects of this agent can be monitored at different scales: from microbial metabolism to the host immune response.

That’s important inside in vitro models of human gut microbiota culture, the use of human-derived microbiota, and the exclusion of host confounders (e.g., diet, stress, medications, host cells) allowed accurate observation of direct microbe-microbe interactions. This approach creates a robust experimental framework for future mechanistic studies on probiotics and microbiome therapies.

Towards a new definition of probiotic efficacy

Huang’s findings et al. have broad implications for the microbiome field. They underline that effective probiotics do not need to dramatically change the microbial composition to achieve meaningful health effects. Instead, maintenance of microbial biomass and maintenance of metabolic function may be the true determinants of resilience.

In this view S. boulardii CNCM I-745 is an example of a next-generation probiotic: a probiotic that protects microbial function, alleviates antibiotic-induced dysbiosis, and contributes to the host immune system without competing with native bacteria or antibiotics themselves.³

As microbiome research continues to advance toward precision and function, this study provides a compelling model for evaluating probiotics through a systems biology lens, linking microbial ecology, metabolism, and immunology in a unified framework.

References:

1. Guarner F, Bustos Fernandez L, Cruchet S, et al. Gut dysbiosis mediates the association between antibiotic exposure and chronic diseases. For Med. 2024; 11:1477882. doi: 10.3389/fmed.2024.1477882.
2. Huang Z, Brot L, Fatouh R, et al. Saccharomyces boulardii CNCM I-745 reduces antibiotic-induced functional changes in the gut microbiome, independent of the host. Intestinal microbes. 2025; 17(1):2575924. doi: 10.1080/19490976.2025.2575924.
3. Waitzberg D, Guarner F, Hojsak I, et al. Can the evidence-based use of probiotics (particularly Saccharomyces boulardii CNCM I-745 and Lactobacillus rhamnosus GG) mitigate the clinical effects of antibiotic-associated dysbiosis? Adv. Ther. 2024; 41(3):901-914. doi:10.1007/s12325-024-02783-3.