Airway adherence of Pseudomonas aeruginosa: mucoexopolysaccharide binding to human and bovine airway proteins

Abstract

The ability of Pseudomonas aeruginosa (PA) to adhere to cells of the upper and lower airways is considered the initial step in its colonization and subsequent infection. Many potential adhesins exist, but few eukaryote receptors have been reported. This study evaluates the adherence of PA and the well-recognized adhesin mucoexopolysaccharide, of the mucoid variant, to tracheal epithelial cells and airway secretions. A number of tools were used to systematically examine this process, each in increasing detail. Scanning electron microscopy of infected tracheal cell monolayers showed that although nonmucoid PA adhered most often as individual organisms, mucoid strains frequently were adherent in the form of clusters of microcolonies. Partially purified mucoexopolysaccharide was itself adherent to the tracheal cell monolayers. More quantitative studies of carbon 14-labeled PA adherence to tracheal cell monolayers demonstrated that (1) bacterial adherence was temperature dependent; (2) mucoid PA was more adherent than nonmucoid PA (p less than 0.005); (3) proteinase treatment of the intact monolayers increased adherence of mucoid PA; and (4) adherence of nonmucoid PA was partially inhibited by pretreatment with N-acetylglucosamine, a normal constituent of airway mucus (control, 9.5 +/- 2.0 bacteria/cell; N-acetylglucosamine, 5.8 +/- 1.5 bacteria/cell; p = 0.05). These observations suggest that N-acetylglucosamine may play a role in the epithelial cell receptor for ligands on the surface of nonmucoid strains of PA. Pretreatment of mucoid PA with N-acetylglucosamine, D-arabinose, D-mannose, or N-acetylneuraminic acid did not affect adherence. Partially purified proteins isolated from the apical plasma membrane of bovine tracheal epithelial cells probed in a Western analysis with the iodine 125-labeled PA mucoexopolysaccharide revealed two binding proteins of 45,000 mol wt and 104,000 mol wt. Human airway secretions of patients with chronic PA infection were screened by the dot blot technique and demonstrated selective binding of mucoexopolysaccharide ligand. Western analysis of these biologically important secretions revealed that PA mucoexopolysaccharide bound to a 65,000 mol wt protein in airway secretions of infected individuals. This glycoprotein is similar to a previously described cell receptor for bacterial type 1 fimbriae.