The alginate produced by Pseudomonas aeruginosa has been reported to play a role in the adhesion of this bacterium to epithelial cell surfaces, although some controversy concerning this role exists. To clarify this controversy, we investigated the ability of alginate to bind to human buccal epithelial cells (BECs) and human tracheal epithelial cells (TECs). Alginate from P. aeruginosa 492c bound to both BECs and TECs. Alginate from strain 492c was found to be multivalent and thus capable of agglutinating both BECs and TECs. The multivalency of alginate complicated the determination of the number of alginate-specific receptors on the BEC and the apparent association constant (Ka). By using the analysis of Hogg and Winzor (Biochim. Biophys. Acta 843:159-163, 1985), an average valency of 2.6 BEC binding domains per alginate molecule was determined, and the maximum binding capacity per BEC was calculated to be 5.8 X 10(-4) micrograms, with a Ka of 4.1 X 10(-2) ml/micrograms. The binding of alginate to immobilized BECs (where only 50% of the BEC surface is exposed) yielded values of 2.52 X 10(-4) micrograms of alginate per BEC for the maximum binding capacity per BEC and a Ka of 3.30 X 10(-2) ml/micrograms. The alginate-specific site on the BEC surface was trypsin sensitive. Alginate from P. aeruginosa 492a did not bind to BECs, differing substantially from that of strain 492c. The data presented here demonstrate that alginate purified from some strains of P. aeruginosa may bind to TECs and BECs in a defined, specific manner, whereas alginate from other strains does not, reflecting structural diversity in P. aeruginosa alginates.
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