Non-pathogenic transient yeast
Broad anti-pathogenic function
Particularly researched for diarrhoea and Candida
Saccharomyces boulardii under the microscope
Saccharomyces boulardii is unique in this database of the world's best probiotic strains, in that it is a non-pathogenic, transient (non-colonising) yeast, originally extracted from the lychee fruit, rather than a bacteria. It is important to note, however, that it is genetically and functionally different from the well-known pathogenic Candida family of yeasts. It was originally classified as a separate species but, after much laboratory testing, it was shown to have certain genomic and structural similarities to Saccharomyces cerevisiae and so is now classified as part of this species. That being said, S. boulardii is a unique microorganism and has vastly different strain-specific properties to other yeasts in the same S. cerevisiae species, in the same way that different strains of bacteria may have completely different actions and properties to other strains within the same species. For more information on the classification of Saccharomyces boulardii, please read our in-depth article.
S. boulardii is the only yeast that has been formally recognised as a probiotic, and it has multiple mechanisms by which it confers benefits to its host. It is recognised as having a broad anti-pathogenic action, due to its sticky outer surface which attaches to pathogenic bacteria such as Escherichia coli and Salmonella, and removes them from the digestive system. As a yeast itself, a much larger micro-organism than a bacterium, S. boulardii is able to effectively compete with and displace harmful yeast strains such as Candida. As part of its survival technique, it also produces anti-fungal substances such as capric, caprylic, and caproic acids, which discourage pathogenic yeasts in its environment.
The boulardii strain is part of the cerevisiae species and the Saccharomyces genus
In addition to this anti-pathogenic action, S. boulardii offers other benefits to its host as it passes through the digestive system. It increases the brush border enzymes in the intestinal wall, e.g. alkaline phosphatases and a-glucosidases, so may help to optimise nutrient absorption. It also secrets an enzyme (leucine aminopeptidase) that helps to prevent allergies to common dietary proteins developing after gut damage resulting from gastroenteritis. Finally, it promotes the secretion of the immunoglobulin secretory IgA (sIgA), a vital part of our immune defences against incoming pathogens and toxins, which helps to downregulate the action of pro-inflammatory cytokines pathways generated in response to pathogenic bacteria, toxins and antigens (Qamar et al, 2001).
Saccharomyces boulardii is one of the most researched probiotics in the world and takes its name from the French scientist, Henri Boulard. Boulard discovered the probiotic yeast in 1923 in South East Asia, where he noticed people using the skin of lychee fruit for its beneficial health properties. S. boulardii is often referred to as S. boulardii lyo, where the 'lyo' is short for 'lyophilisation' - a form of freeze-drying which S. boulardii normally undergoes in its supplement form. This process allows the supplement to be shelf-stable so that refrigeration is not necessary.
Saccharomyces boulardii – Safety and Survival
Saccharomyces boulardii is a food supplement commonly used in Europe with research demonstrating its safety and survival to reach the gut alive. There have been numerous meta-analyses of this probiotic yeast to determine efficacy and safety (Mc Farland, L., 2010; Kelesisis, T. & Pothoulakis, C., 2012). It has been deemed safe and well tolerated in many clinical trials, however it should be noted that those who are severely immune compromised or those requiring central venous catheters are advised to only take this strain under medical supervision, as in rare cases fungaemia has been reported.
S. boulardii has been isolated in stools when taken orally, as assessed by Klein, S. M. et al., (1993) who identified recovery in the stool in a dose dependant manner, and Blehaut, H. et al., (1989). This indicates that S. boulardii survives to reach the gut alive.
Saccharomyces boulardii and Diarrhoea
Saccharomyces boulardii is probably best known for its potential to relieve diarrhoea symptoms; it has been found to reduce antibiotic-associated diarrhoea (AAD), traveller’s diarrhoea, IBS-D, and acute or chronic diarrhoea in children and in adults. Its anti-diarrhoeal properties are so well-recognised and researched that it is used routinely as an anti-diarrhoeal medicine in many hospitals around the world. Saccharomyces boulardii is actually a registered medicine in over 100 countries in the world, under the brand name Florastor.
McFarland, L. V. (2010) conducted a systematic review and meta-analysis of Saccharomyces boulardii in adult patients, looking at the efficacy and safety of Saccharomyces boulardii (S. boulardii) for various disease indications in adults. This was based on the peer-reviewed, randomised clinical trials and pre-clinical studies from the published medical literature between 1976 and 2009. This review of 31 randomised, placebo-controlled treatment arms in 27 trials (encompassing 5029 study patients), found S. boulardii to be significantly effective and safe in 84% of those treatment arms. A meta-analysis found a significant therapeutic efficacy for S. boulardii in the prevention of antibiotic-associated diarrhoea. Saccharomyces boulardii can therefore be strongly recommended for prevention of AAD, as well as for traveller’s diarrhoea and the prevention of nutrition-related diarrhoea; also for the alleviation of Helicobacter pylori infection and related symptoms.
To further demonstrate the efficacy of S. boulardii for the prevention of antibiotic-associated diarrhoea symptoms, a total of 269 children with otitis media (an inflammatory disease of the middle ear), and/or respiratory tract infections were enrolled to take part in a randomised, double-blind, placebo-controlled trial. For the purposes of the trial, one group of children was given antibiotic treatment, along with a supplement containing 5 billion CFU of S. boulardii, whilst another group was given the antibiotic treatment along with a placebo supplement. The results indicated that the group taking the probiotic had a lower incidence of diarrhoea than the group taking the placebo (Kotowska et al., 2005).
A further related double-blind, placebo-controlled trial was conducted with the participation of 130 children aged 3 months to 3 years, all of whom were suffering with diarrhoea symptoms. The group of children was divided into two sub groups, a treatment group being given a supplement containing 400 million CFU of Saccharomyces boulardii dissolved in 5mg of liquid and the second control group given a liquid placebo supplement. The results showed that S. boulardii made a significant impact on the rate of recovery from diarrhoea. The method of action was identified as its inhibitory effect on the growth of pathogenic strains (Cetina-Sauri, 1994).
Graph 1 - shows S. boulardii can significantly reduce recovery time from diarrhoea
A study (Wan et al 2017) on children was run to test the efficacy and safety of S. boulardii in preventing AAD in 1-3 year old children - 408 cases divided into groups. One being given S. boulardii alongside antibiotics, and the other not. Whilst on antibiotics, the incidence of AAD in prevention group was 10.3% (22 cases) which was significantly lower than that of control group 29.2% (57 cases). Additionally, post antibiotics a difference was also seen, with new cases of diarrhea in prevention group being 2.4% (5/213) which was significantly lower than that in control group 16.4% (32/195).
In another trial, 60 children with watery diarrhoea and the rotavirus were randomised into a control and test group. The test group was given S. boulardii for 5 days. The result was that the average duration of diarrhoea was shorter in the intervention group (60 vs 89) and there was also a significantly shorter duration of hospital stay (74 vs 91) (Das S, et al., 2016).
A 2021 meta-analysis of 84 studies involving 13,443 children found that certain single-strain probiotics effectively treated acute diarrhea in children with various certainty evidence. Researchers concluded that among all probiotics, Saccharomyces boulardii may be the most effective in reducing both duration of diarrhea (compared with placebo) and risk of diarrhea lasting ≥2 days (compared with placebo or no treatment), with moderate evidence. (Zengbin L, et al., 2021)
Further relevant studies: Abbas et al (2014), Akil et al (2006), Bruggengate (2015), Burande (2013), Can et al (2006), Canani et al (2007), Cindoruk M., (2007), Corrêa et al (2011), Cremonini et al. (2002), Dinleyici et al., (2015), Doron et al., (2008), Duman et al., (2005), D'Souza A. et al., (2002), Eren et al (2010), Fidan I. et al., (2009), Gaón D.l. et al., (2003), Gotteland M. et al., (2005), Grandy G. et al., (2010), Hafeez et al (2002), Hochter W. et al., (1990), Htwe K. et al. (2008), Hurduc et al. (2009), Kabir et al (2009), Kirchhelle A. et al., (1996), Kurugol Z. & Koturoglu, G. (2005), Le Luyer B. et al., (2010), Maupas J.L. et al., (1983), Shan et al., (2013), Sudha M.R. et al., (2012), Szajewska H et al (2005), Zhang DM, et al (2017), Zhao et al (2014), Zojaji H., (2013).
Saccharomyces boulardii and Candida
Saccharomyces boulardii is widely used as a ‘yeast against yeast’ strategy to help inhibit the overgrowth of Candida yeasts in the body. The Candida genus of yeasts are natural residents of the human body; however, when conditions are appropriate for their proliferation, they can multiply and cause yeast infections known as Candidiasis (thrush).
Research indicates that S. boulardii secretes capric, caprylic, and caproic acids which inhibit the hyphae formation on the Candida yeast, preventing it from multiplying. It also reduces Candidial adhesion and biofilm formation, again reducing its ability to thrive and grow (Murzyn et al., 2010). A study showed that both S. boulardii, significantly inhibited Candida albicans adhesion to epithelial cell lines. The IL-8 gene expression by C. albicans-infected Caco-2 cells was suppressed by the addition of S. boulardii. These results indicate that S. boulardii affects C. albicans adhesion and reduces cytokine-mediated inflammatory host response. (Murzyn A. et al., 2010)
A prospective, randomised, comparative study was conducted on a total of 181 preterm infants with a gestational age of less than 32 weeks, and a birth weight of less than 3.3lbs. They were randomised into two groups, to receive either S. boulardii or the anti-fungal nystatin. Weekly skin and stool cultures were performed to determine colonisation, and weekly blood cultures taken to check for invasive infections. Two patients had Candida-positive blood cultures in the nystatin group, whereas no evidence of Candida was seen in the probiotic group. Additionally, feeding intolerance and clinical sepsis were significantly lower in the probiotic group than in the nystatin group (Demirel, et al., 2013).
NB: S. boulardii is not always recommended for those under the age of 1. Check with your probiotics supplier before giving to infants.
Further relevant studies: Algin C., et al. (2005), Berg et al., (1993), Berg R. et al., (1993), Ducluzeau, R., (1982), Jawhara, S., (2007), Kumar S. et al., (2013), Krasowska A. et al., (2009), Lherm T. et al., (2002), McFarland L. V., (2010), Tomičić, Z. et al., (2016).
Saccharomyces boulardii and Clostridium difficile Infection
The term antibiotic-associated diarrhoea (AAD) refers to a benign, self-limiting diarrhoea which often manifests following the use of antibiotics. Usually, no pathogens are identified and the diarrhoea is caused by changes in the balance and function of the gut flora. On the other hand, though it often occurs in connection with antibiotic use, _Clostridium difficile i_nfection causes diarrheal illnesses due to the toxins produced by this gram-positive anaerobic pathogenic bacteria.
A review of four studies conducted by Tung et al. (2009) assessed the effects of Saccharomyces boulardii on Clostridium difficile infection_._ Two of the studies considered cases of recurrent C. difficile issues in patients, and the other two studies looked at primary prevention of the infection in patients taking antibiotics. Although the first two studies yielded some interesting results and showed some positive trends occurring as a result of supplementation with S. boulardii, the second two studies failed to offer statistically relevant results. The review concluded, therefore, that S. boulardii may be effective for secondary prevention of C. difficile, and helps to prevent recurrence; however, more research is needed in order to ascertain its potential role in primary prevention of the infection. A similar conclusion was reached in a review by Surawicz (2003), who also suggested that there may be a role for S. boulardii as an adjunct in the treatment of recurrent Clostridium difficile- associated disease.
Further relevant studies: Buts J. et al., (1993), Castagliuolo I. et al., (1999), McFarland L.V., (2010), Pothoulakis, C. et al., (1993), Surawicz, C.M. et al., (1989), Surawicz, C.M. et al., (2000), Surawicz, C.M., (2003).
Saccharomyces boulardii and Inflammatory Bowel Disease (IBD)
A significant role for the gut microflora in the pathogenesis of inflammatory bowel disease is now being identified, although the mechanisms involved are not fully understood (Guslandi M. et al., 2003). The possible therapeutic mechanisms of probiotics in intestinal inflammatory disorders include: antagonism against enteric pathogens; strengthening of the gut mucosal barrier; inhibition of the local secretion of inflammatory mediators; and stabilisation of local immunological activity (Kelesidis T 2012).
Guslandi et al. (2003) looked at the effect of S. boulardii on 25 patients with IBD, who were experiencing mild to moderate flare-ups of Ulcerative Ulcerative Colitis. To test the effects of the probiotic, the patients received 5 billion of S. boulardii in addition to their treatment of Mesalazine. A successful outcome was achieved in 17 of the patients. The authors concluded that the Saccharomyces boulardii did induce remission in the patients; however, due to the lack of a control group for comparison, more research is needed to further substantiate these results.
Further relevant studies: Bafutto et al (2013), Choi et al (2011), Garcia et al (2008), Garrido-Mesa J. et al., (2015), Guslandi M. (2000), Kabir et al (2011), McFarland L. V., (2010), Thomas S. et al., (2011), Pineton de Chambrun (2015).
Saccharomyces boulardii and H. pylori
Chronic infection with H. pylori can be a risk factor for ulcer disease, gastric adenocarcinoma not to mention painful. Therefore, eradication of H. pylori is a primary goal in patients that are symptomatic. The eradication rates achieved by classic triple therapy consisted from proton pump inhibitor and double antibiotic therapy are quite low and range from 60% to 80% This is due to resistance to antibiotics and to moderate patient compliance. Antibiotic-associated gastrointestinal side effects are a major cause for lower compliance.
Bin et al (2015) this trial looked at 194 children who were H. pylori positive. Saccharmoyces boulardii as given to the treatment group, and the control group was given a placebo. In the test group diarrhea occurred in 12 cases (11.76%), starting after approx. 6.25 days, lasting 3.17 days, and compliance with eradication treatment was 100%. In the control group, diarrhea occurred in 26 cases (28.26%), starting after 4.05 days, lasting 4.02 days, and in six cases eradication treatment was stopped prematurely. The researchers concluded therefore that Saccharomyces boulardii, although wouldn’t eradicate H. pylori on its own would help by reducing bacterial load and probably increase eradication rate due to increasing compliance to treatment. S. boulardii is, therefore, a useful adjuvant.
Further relevant studies: Homan & Orel (2015), Namkin et al (2016)
Saccharomyces boulardii and Human Immunodeficiency Virus (HIV)
The anti-inflammatory potential of S. boulardii has attracted some attention in the field of probiotic research, and a particularly interesting study to demonstrate this activity was conducted with the co-operation of a group of HIV-positive patients. Imbalances in the gut microbiota are particularly concerning in such vulnerable groups of patients; gut dysbiosis has been linked to increased microbial translocation resulting in chronic inflammation in HIV patients.
A trial looked at the impact of probiotic supplementation on the composition of the gut microbiome (tested via faecal samples) in 44 HIV patients, who had been randomised to receive either S. boulardii or a placebo for three months. Compared to the placebo group, patients taking the probiotic had lower levels of some gut bacteria species, which were associated with systemic levels of bacterial translocation and inflammation markers. The authors concluded that Saccharomyces boulardii is able to benefit the gut microbe composition and systemic inflammation in HIV patients (Villar-Garcia J. et al, 2017).
Further relevant studies: Villar-Garcia J. et al (2015).
Saccharomyces boulardii and Parasites
Research into the treatment of parasites with probiotics is still in its infancy, however, there is some evidence to suggest that Saccharomyces boulardii may be beneficial to those with a parasitic infection.
Further relevant studies: Dinleyici et al. (2009), Dinleyici (2011), Mansour-Ghanaei et al. (2003).
As some properties & benefits of probiotics may be strain-specific, this database provides even more detailed information at strain level. Read more about the strains that we have included from this genus below.
Saccharomyces strain: Saccharomyces cerevisiae boulardii.