The mucoid exopolysaccharide of Pseudomonas aeruginosa is thought to confer antiphagocytic properties on mucoid strains of P. aeruginosa, thus allowing them to persist in the respiratory tract. It has also been speculated that the mucoid exopolysaccharide may be the adhesin for mucoid strains, but proof is lacking. We studied the role of the mucoid exopolysaccharide in adherence of mucoid strains in competitive experiments with purified mucoid exopolysaccharide, by measuring the binding of 14C-labeled mucoid exopolysaccharide to injured tracheas and testing whether an antibody against the major epitope of the mucoid exopolysaccharide inhibits adherence of these organisms. Our data show that the purified mucoid exopolysaccharide increased the adherence of four of the mucoid strains tested (by 50 to 300%; P less than 0.001) instead of inhibiting adherence. Radiolabeled mucoid exopolysaccharide bound much better to injured tracheal cells than to normal tracheal cells (P less than 0.001), and antibody against the antigen of strain 2192, the strain from which mucoid exopolysaccharide was prepared, inhibited the adherence of four of five mucoid strains but not the strain lacking this antigen. This antibody also failed to inhibit a nonmucoid revertant from strain 2192, which was previously shown to be inhibited by pili. These data strongly support the thesis that the mucoid exopolysaccharide is the adhesion for mucoid strains of P. aeruginosa.
