Saccharomyces cerevisiae (Boulardii) is a non-pathogenic, gut-friendly yeast found in the human digestive tract. Commonly known as SB, it features in many popular probiotic and gut health products around the world, and has been proven to protect the gut lining.[1][2]
Being a probiotic yeast, it shares many similarities with probiotic bacteria, but there are some differences. The fact that SB is unaffected by antibiotics,[3] is a major differentiator and something that not many bacterial probiotics can boast. This allows it to be safely co-prescribed alongside antibiotics, with the two forming a potent partnership. The yeast even minimises the common occurrence of antibiotic-associated diarrhoea. Indeed, SB is best known for its prevention and treatment of various diarrheal conditions.[4][5]
Furthermore, SB thrives at regular human body temperature,[6] and is fine in acidic environments such as the stomach, which can kill many bacterial probiotics.[7]
If all of this sounds too good to be true, fear not! Scientific research backs it up. If what you’ve read leaves you curious to learn more about this superhero yeast and how to harness its full potential, read on!
Discovery
The discovery of SB is part of probiotic folklore. While visiting Indochina during the cholera outbreak of 1920, French microbiologist Henri Boulard noticed some of the locals were drinking tea made from the skins of lychee or mangosteen. The realisation that these people were suffering less diarrhoea led him to investigate the skins and this stimulated the subsequent discovery of an inherent yeast, which he eventually named “Saccharomyces boulardii”.[8]
Figure 1. Structure and shape of Saccharomyces boulardii
The Role of Yeasts in the Gut Microbiome
Although the microbiome consists mostly of bacteria, yeasts and other fungi and are known to play an important role in the stability of the microbial environment.[9][10] For instance, various fungi have been shown to influence the immune system, either dampening or promoting inflammatory responses.[11]
Although many fungi are considered typically pathogenic, others have a beneficial impact on the microbiome and gut health in general.[12][13]
Studies have revealed that Saccharomyces cerevisiae and Saccharomyces boulardii are associated with positively modulating the proportion of important bacterial communities in the gut microbiota.[14][15] Research confirms that SB can act as a surrogate to support the restoration of a normal microbiome following antibiotic treatment.[16] Furthermore, a similar modulating effect on microbial composition has also been demonstrated in Inflammatory Bowel Disease (IBD).[17][18]
Figure 2. Saccharomyces boulardii interacting with the gastrointestinal epithelium
Anti-microbial Superpowers
The most notable impact SB has on the gut is its inhibitory capacity against pathogens which cause diarrhoea. SB boasts research-confirmed effectiveness against Salmonella,[19] Clostridium difficile,[20] Helicobacter pylori,[21] and Candida albicans[22] amongst a host of other bad guys.[23]
This superpower is exemplified by its production and secretion of specific peptides and enzymes which destroy microbial toxins, including that of E. coli.[24][25][26] SB even acts as a decoy, in order to bind with toxins and block their receptor sites.[27][28] Another trick it possesses is an ability to produce high amounts of acetate which reduces the gut pH and effectively inhibits prominent pathogens.[29] And if this isn’t enough, SB impedes pathogenic microbes from attaching to intestinal receptor sites and this facilitates their eviction from the gastrointestinal tract.[30]
SB and Antibiotics – a Dynamic Duo
Unlike most probiotics, SB excels alongside antibiotics. A 2022 placebo-controlled trial assessed the efficacy of SB alongside the antibiotic azithromycin. Children admitted to hospital for acute colitis all received azithromycin, while half of them also received SB. The children receiving the SB had fewer episodes of diarrhoea and shorter hospital stays than the children solely on the antibiotic.[31]
Despite being life-saving medicines, there is also a down-side to antibiotics. Their overall detrimental effect on the microbiome is well-documented, however, the phenomenon of antimicrobial resistance is fast becoming a frightening reality. Governments worldwide[32][33] are anxiously trying to limit the situation, with the potential ramifications projected to cost 8.2 million lives globally in 2050.[34]
With this in mind, researchers investigated a combination of probiotics including SB to see whether they could prevent drug resistant bacteria after a course of antibiotics. The investigators found that the probiotic did in fact lead to a significant decline in colonisation after the antibiotic course. In contrast, no significant changes were observed in the placebo group.[35]
Immune Champion
The effect of this yeast on the immune system has also been investigated and once again, SB shines. Various studies have shown that SB modulates immune responses towards a more activated state. This increases early resistance to infections both within the gut and throughout the body. It is also able to modulate pro- and anti-inflammatory responses via chemical mediators affecting immune cells.[36]
Administration of SB increases levels of the IgA antibody, which plays a crucial role in the immune function of mucous membranes lining the gut.[37][38] IgA binds to pathogenic bacteria and facilitates their excretion via feces. SB also significantly increases specific immune lymphocytes and modulates others.[39][40] Furthermore, SB is able to stimulate IgM antibodies, as well as macrophages, which assist in clearing pathogenic infections from the gut.[41]
Get a Gut Superhero on Your Side!
SB is a real probiotic superhero. From its direct pathogenic bad guy bashing to its intuitive immune system modulation, SB defends your gut like no other. It’s proficiency at surviving passage through the gastrointestinal tract, which is a difficult ask for many bacterial probiotics, is only chapter one of this amazing story. It’s ability to withstand the effects of antibiotics, and even work alongside them to further eliminate harmful bacteria, is further proof of the incredible power it possesses.
So, if you’re perturbed by pesky pathogens, if you’re sick of slimy suspects, or you’ve had enough of malicious microbes, get a true probiotic superhero on your side… Get some SB into you, and feel the difference. Your gut will thank you for it!
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