Studies on the Adherence Properties of Plant Lectins and Bacterial Adhesins and their Inhibition by Prebiotic Oligosaccharides and Bovine Colostrum Fractions

Prebiotic carbohydrates, in addition to their ability to influence the colonic microbiota, are also able to interfere with how pathogenic bacteria attach to the epithelial cells that line the intestinal tract. For Salmonella, Escherichia coli, and other enteric pathogens, adherence is a receptor-mediated event between bacterial adhesins and their complementary ligands located on the mucosal surface. Some prebiotic carbohydrates are structurally similar to these ligands and inhibit lectin binding. However, the mechanism for this inhibition is not well understood, in part because the receptor sites on the target cells have not been identified. The goal of this research was to measure the effect of two prebiotic carbohydrates, galactooligosaccharide (GOS) and polydextrose (PDX), on the binding kinetics of lectins to epithelial tissue culture cells. To measure adherence, fluorescent-labeled lectins (ConA, WGA, PNA, RCA and ECL) were added individually to cover slips containing HEp-2 tissue culture cells. In some treatments, either the cognate ligand or a prebiotic was added; unbound reactants were removed by washing. Photographs were taken by fluorescence microscopy and the images were analyzed to quantify the spectral component. All the lectins that were able to bind to the target cells were inhibited by nearly 100% in the presence of 1 mg/ml of the cognate ligands. When prebiotics were added (up to 100 mg/ml), inhibition of lectin binding also was observed, depending on the structural similarity between the prebiotic and the cognate ligands. In particular, GOS significantly inhibited attachment of all the lectins except for WGA. In contrast, PDX did not significantly inhibit attachment of the lectins (with the exception of WGA), suggesting that it is structurally dissimilar to the HEP-2 receptor sites. The results from this research support the role of GOS as an anti-adherence agent and also suggest that the receptor sites located on the surface of epithelial HEp-2 cells are structurally similar to GOS. In conclusion, the proposed mechanism of bacterial binding inhibition caused by active oligosaccharides was confirmed.