Competition for adhesion between probiotics and human gastrointestinal pathogens in the presence of carbohydrate

The adhesion of Lactobacillus rhamnosus GG to human enterocyte-like Caco-2 cells was not inhibited by eight carbohydrates tested, namely N-acetyl-glucosamine, galactose, glucose, fructose, fucose, mannose, methyl-alpha-D-mannopyranoside and sucrose. The degree of hydrophobicity predicted the adhesion of L. rhamnosus GG to Caco-2 cells. L. rhamnosus GG, however, was able to compete with Escherichia coli and Salmonella spp. of low hydrophobicity and high adhesin-receptor interaction for adhesion to Caco-2 cells. The interference of adhesion of these gastrointestinal (GI) bacteria by L. rhamnosus GG was probably through steric hindrance, and the degree of inhibition was related to the distribution of the adhesin receptors and hydrophobins on the Caco-2 surface. A Carbohydrate Index for Adhesion (CIA) was used to depict the binding property of adhesins on bacteria surfaces. CIA was defined as the sum of the fraction of adhesion in the presence of carbohydrates, with reference to the adhesion measured in the absence of any carbohydrate. The degree of competition for receptor sites between Lactobacillus casei Shirota and GI bacteria is a function of their CIA distance. There were at least two types of adhesins on the surface of L. casei Shirota. The study provides a scientific basis for the screening and selection of probiotics that compete with selective groups of pathogens for adhesion to intestinal surfaces. It also provides a model for the characterisation of adhesins and adhesin-receptor interactions.