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

To initiate colonization and infection, most microbial pathogens must first recognize and adhere to cells in the host tissues. Adherence inhibition, therefore, can be used as a strategy for preventing infectious disease. In this research, we developed a simplified model using plant lectins and HEp-2 tissue culture cells to simulate bacterial adhesins-receptors interactions. The effect of lectin ligands and two prebiotic carbohydrates, galactooligosaccharide (GOS) and polydextrose (PDX) was measured with this approach. Lectins that were able to bind to the target cells were inhibited in the presence of the cognate ligands and at least one of the prebiotic carbohydrates. The inhibition was generally proportional to the structural similarity between the prebiotic and the cognate ligands. In particular, GOS significantly inhibited attachment of most of the lectins, consistent with the established role of GOS as an anti-adherence agent. The results support the hypothesis that cell binding inhibition is caused by competition of the GOS for the lectin. Experiments were completed to assess the anti-adherence properties of several bovine colostrum fractions against Escherichia coli, Cronobacter sakazakii and Salmonella enterica serovar Typhimurium. An ultra-filtration permeate and an oligosaccharide fraction significantly inhibited binding of all four pathogens to HEp-2 cells. In contrast, a nano-filtration retentate inhibited Salmonella adherence, but not other pathogens, while a colostrum whey fraction had no effect for any of the test organisms. The effectiveness of the inhibitory fractions was mainly attributed to the presence of oligosaccharides and/or peptides. Several methods for extracting oligosaccharides and removing lactose from bovine colostrum were evaluated. Enzymatic hydrolysis and microbial fermentation were effective methods for degrading lactose. In contrast, the physical-chemical separation methods were limited in their ability to separate and enrich oligosaccharides. The results obtained from this study provide evidence to support the concept that bovine milk components can promote consumer health. These constituents could be used as antimicrobial agents in foods and/or in pharmacological applications. In particular, bovine colostrum whey appears to be a suitable source for these bioactive compounds. Advisor: Robert W. Hutkin