Intestinal pathogen binding effects are related to mannanoligocaccharides that occur in several micro-organism species e.g. fungi and yeasts. Binding varies between species depending on their size, structure and cell wall properties. The purpose of the study was to elucidate differences in adherence potential of commercially used yeast cells and possibly determine causative elements for the observed differences. Electron microscopy and surface hydrophobicity measurements reveal that Pichia guilliermondii yeast possesses distinguished traits compared to Saccharomyces cerevisiae that may account for observed differences in pathogen binding efficiency. Pichia guilliermondii significantly inhibited adherence of pathogenic strains of Escherichia coli and Salmonella enterica in small intestinal epithelium of swine and broiler chicken. Treatment of Pichia yeast with digestive fluids significantly increased this effect. In-vivo, gastric activation occurs naturally as verified by broiler assays with P. guilliermondii. P. guilliermondii and S. cerevisiae retained their inhibitory effects on pathogenic E. coli adherence after passing through the upper digestive tract. Jejunal digesta recovered from birds treated with P. guilliermondii showed higher inhibitory effect than digesta from birds treated with the S. cerevisiae yeast. The inhibitory effect was still detectable in ileal digesta. Intact, non-gastric treated P. guilliermondii was as effective as the gastric pre-treated yeast, suggesting that digestive enzymes of broiler chicken were capable of activating yeast cells in-situ.