Adhesion studies for probiotics: need for validation and refinement

Adhesion of probiotic bacteria to intestinal epithelial cells is regarded a s a prerequisite to exert beneficial health effects. Human intestinal epith elial lines, like Caco-7 or HT-29 cells, have been extensively used to sele ct for adhesive strains in vitro. Adhesion to intestinal mucus has been use d to a res ser extent. However, to date, there has been no standardization of the conditions used in in vitro adhesion assays. As a consequence, resul ts obtained in different laboratories using identical strains, but differen t assay conditions, show great variability. This lack of standardization co mplicates the interpretation of data and discrepancies emerge on what is me ant by effective adhesion. A critical validation of in vitro adhesion is es sential for the food industry, using adhesion assays as predictive screenin g tools to assess new probiotic strains. In this review we summarize a comp arative study on adhesion of the well characterized probiotic bacteria L. j ohnsonii La1 and L. rhamnosus CC with respect to the influence of bacterial growth conditions, growth phase, buffer, pH, and mucus on adhesion propert ies. The results are employed in the current scientific discussion to allow a critical evaluation on the reliability of the in vitro assays. (C) 2000 Elsevier Science Ltd. All rights reserved.