What Does Saccharomyces Boulardii + MOS Do? Saccharomyces Boulardii+MOS contains the probiotic yeast Saccharomyces boulardii, which survives passage through stomach acid and delivers its benefits to the intestinal tract. This strain helps protect and maintain a normal intestinal microflora. It also works to restore the normal intestinal microflora when possible disruptions may occur, such as during travel or the intake of certain medications. MOS (MannanOligoSaccharides) is an oligosaccharide from the cell walls of S. cerevisiae that can discourage bacteria from adhering to the epithelial cells and reduce their proliferation.