By Manuela Gottardi
When we talk about yeasts we might think of bread, beer and wine but nowadays when associated with human health, yeasts are often seen as pathogens. The term yeast is very general and it is important to take into account that it comprises a wide variety of microorganisms of different species of which some are pathogens.
As you might be aware of, our gastrointestinal tract (GIT) is colonized by hundreds of millions of microorganisms representing our gut microbiota. They are non-pathogenic and the GIT is their perfect environment to live in. Mostly, the relationship between host and the intestinal microbiota is mutually beneficial as we also take advantage of it. In fact, our microbiota exerts several necessary functions for our development and health. It is involved in the development of the immune system, it has protective functions against pathogens by acting as a mechanic barrier but also provides us with vitamins (O’ Hara et al., 2006; Shanahan, 2002).
When the intestinal microbiota is unbalanced by some health issues (i.e. Inflammatory bowel disease?, Crohn’s disease) or the usage of antibiotics to treat other conditions, using prebiotic or probiotic formulations is helpful to restore an equilibrated composition of the microbiota.
According to World Health Organization, probiotics are “live micro-organisms which, when administered in adequate amounts, confer a health beneﬁt on the host”. Mostly they are composed by a mixture of Lactobacilli and Bifidobacteria species but also the yeast Saccharomyces boulardii is found to be an effective probiotic.
S. boulardii was initially found in Indochina and it is not originally part of the human microbiota. In 1923, the French scientist Henri Boulard noticed that during a Cholera epidemic some of the population was refractory to the symptoms. He found out that some locals used to drink tea made out of lychee and mangosteen, from where he later was able to isolate S. boulardii (Palma et al., 2015).
S. boulardii is able to sustain the low pH of the stomach and to reach the intestine alive, moreover it is resistant to antibiotics, therefore can be combined to antibiotic treatments. One concern related to bacterial probiotics is the horizontal transfer of antibiotic resistance genes among bacteria. Therefore they are able to transfer this genetic information also to pathogenic bacteria. Since horizontal transfer does not happen between yeast and bacteria, S. boulardii is not risky regarding this aspect , which is nowadays of great importance.
S. boulardii has been proven to be an effective probiotic in studies in animals and humans, especially preventing antibiotic associated diarrhea (AAD). The studies were performend on hospitalized patients though randomized trials in order to prevent AAD. The majority of the trials turned out to show positive effects on patients treated with S. boulardii in comparison to controla patients(D. Czerucka et al, 2007; McFarland 2010; Everard et al., 2014).
Studies also tested the efficacy of S. boulardii against traveller’s diarrhea, irritable bowel syndrome, inflammatory bowel disease or other types of diarrhea (D. Czerucka et al, 2007; McFarland 2010).
Yeast as probiotics is still a field that needs to be further investigated and so far S. boulardii is the only yeast commercialized as probiotic but there is certainly room for new developments.
D. Czerucka, T. Piche, P. Rampal (2007) – Review article: yeast as probiotics – Saccharomyces boulardii Aliment Pharmacol Ther 15;26(6):767-78.
A. Everard, S. Matamoros, L. Geurts, N.M. Delzenne, P.D. Cani. (2014) – Saccharomyces boulardii administration changes gut microbiota and reduces hepatic steatosis, low-grade inflammation, and fat mass in obese and type 2 diabetic db/db mice. MBioJun 10;5(3):e01011-14.
L.V. McFarland 2010 – Systematic review and meta-analysis of Saccharomyces boulardii in adult patients World J Gastroenterol May 14; 16(18): 2202-2222.
A.M. O’ Hara, F. Shanahan (2006) – The gut flora as a forgotten organ. EMBO Reports 7: 688-693.
M.L. Palma, D. Zamith-Miranda, F.S. Martins, F.A. Bozza, L. Nimrichter, M. Montero-Lomeli, E.T. A. Marques Jr, B. Douradinha (2015) – Probiotic Saccharomyces cerevisiae strains as biotherapeutic tools: is there room for improvement? Appl Microbiol Biotechnol.
F. Shanahan (2002) – The host-microbe interface within the gut. Best Pract Res Clin Gastroenterol 16(6):915-931.