01 Saccharomyces boulardii

Saccharomyces cerevisiae var boulardii (S.boulardii) is a fungal probiotic which has been deeply studied at present. S.boulardii was discovered and isolated from Indonesian fruit lychee by French microbiologist Henri Boulard in 1923. In 1962, the strain was used as a prescription drug to treat human diarrhea. Unlike Saccharomyces cerevisiae, S.boulardii lacks the ability to utilize galactose and form spores, so it has always been considered an independent species under the genus Saccharomyces. With the development of molecular germline genetics in recent years, S.boulardii has also been re-identified as a subspecies of Saccharomyces cerevisiae [1-2].

02 The probiotic principle of S.boulardii

Although the specific mechanism of action is not clear at present, a large number of experimental studies have proposed the following potential principles [3-4]:

(1) The role of S.boulardi cells in adsorbing toxins. The flagella of Escherichia coli or Salmonella can secrete an exotoxin, which makes the flagella adsorb on the mannose residues of intestinal epidermal cells, which is the main cause of intestinal cell pathology. The mannose oligosaccharides on the outer cell wall of S.boulardi can competitively aggregate the flagella of these pathogens, so that E. coli and Salmonella cannot adhere to the intestinal cells. Studies have shown that each S.boulardi cell can adsorb about 200 E. coli and other pathogenic bacteria with adherent toxins.

(2) S.boulardi cells can secrete proteases, which can degrade toxin A and toxin B produced by Clostridium, thereby inhibiting the effect of toxins on intestinal epidermal cells. Studies have shown that S.boulardi can degrade pathogenic bacteria's toxins and adhesion site receptors to protect them from pathogenic bacteria.

(3) The glucan in the cell wall of S.boulardi can significantly increase the synthesis of secretory immunoglobulin A (sIg A) in the small intestine, and sIg A can combine with viral antigens to reduce the multiplication of pathogenic bacteria on the intestinal mucosa.

(4) The activity of S.boulardi in the gastrointestinal tract can lower the pH in the intestinal tract, improve the intestinal environment, inhibit the reproduction of harmful bacteria, and facilitate the growth of probiotics.

(5) Active yeast can activate zinc-binding metalloprotease activity, thereby stimulating the secretion of brush border disaccharase.

(6) Anti-inflammatory effect. S.boulardi can effectively prevent inflammation during diarrhea.

03 The application of S.boulardi

Nowadays, S.boulardi as a probiotic is mainly used in medicine and feed production. In medicine, it is mainly used to treat diarrhea. Its safety and effectiveness have been studied and confirmed. It has good clinical effects in the treatment of antibiotic-related diarrhea, recurrent Clostridium difficile disease, traveler's diarrhea, rotavirus diarrhea and inflammatory bowel disease [5].

In terms of feed applications, S.boulardi has a very good effect on diarrhea caused by microbial infections and biological toxins. The cells are rich in nutrients and functional substances such as protein, vitamins and nucleic acids, which can enhance the body’s immunity, maintain the balance of the gastrointestinal microenvironment, promote the digestion and absorption of nutrients in the animal’s gastrointestinal tract, and further improve the animal’s production performance. Its application as a feed additive has been recognized by many countries (regions) in the world including China and the European Union, and has broad application prospects in animal husbandry. Although the abundance of yeast in the intestinal flora is small, its cell size is more than 10 times that of bacteria, so it has obvious steric hindrance. Studies have found that the addition of S.boulardi to sows during pregnancy and lactation can significantly reduce the number of Escherichia coli and Clostridium perfringens in the intestines, effectively improve constipation during lactation, increase feed intake during lactation, and weaning weight and average daily gain of piglets at 21 days of age [6].

References:

[1] Khatri I, Tomar R, Ganesan K, et al. Complete genome sequence and comparative genomics of the probiotic yeast Saccharomyces boulardii[J]. Scientific Reports, 2017, 7(1): 371.

[2] Jonkers D, Stockbrugger R. Review article: Probiotics in gastrointestinal and liver diseases[J]. Alimentary Pharmacology and Therapeutics, 2007, 26(s2): 133-148.

[3] 方晨. 布拉迪酵母微囊华包埋技术的研究[D]. 武汉轻工大学, 2015.

[4] 董运海，张海波，陈智仙，等. 布拉氏酵母对抗生素相关腹泻作用的研究进展[J]. 国外医药（抗生素分册）, 2019, 40(01): 50-55.

[5] 楚杰，王凤山，张大伟. 布拉酵母菌的生物学作用及防治疾病应用研究进展[J]. 药物生物技术, 2006, (1): 71-73.

[6] 龙广，魏宏逵，彭健. 布拉迪酵母菌的研究进展及其在母猪生产中的应用[J]. 饲料工业, 2016, 37(20): 34-37.