BopA Does Not Have a Major Role in the Adhesion of Bifidobacterium bifidum to Intestinal Epithelial Cells, Extracellular Matrix Proteins, and Mucus
ABSTRACTThe ability of bifidobacteria to adhere to the intestine of the human host is considered to be important for efficient colonization and achieving probiotic effects.Bifidobacterium bifidumstrains DSM20456 and MIMBb75 adhere well to the human intestinal cell lines Caco-2 and HT-29. The surface lipoprotein BopA was previously described to be involved in mediating adherence ofB. bifidumto epithelial cells, but thioacylated, purified BopA inhibited the adhesion ofB. bifidumto epithelial cells in competitive adhesion assays only at very high concentrations, indicating an unspecific effect. In this study, the role of BopA in the adhesion ofB. bifidumwas readdressed. The gene encoding BopA was cloned and expressed without its lipobox and hydrophobic signal peptide inEscherichia coli, and an antiserum against the recombinant BopA was produced. The antiserum was used to demonstrate the abundant localization of BopA on the cell surface ofB. bifidum. However, blocking ofB. bifidumBopA with specific antiserum did not reduce adhesion of bacteria to epithelial cell lines, arguing that BopA is not an adhesin. Also, adhesion ofB. bifidumto human colonic mucin and fibronectin was found to be BopA independent. The recombinant BopA bound only moderately to human epithelial cells and colonic mucus, and it failed to bind to fibronectin. Thus, our results contrast the earlier findings on the major role of BopA in adhesion, indicating that the strong adhesion ofB. bifidumto epithelial cell lines is BopA independent.