Usefulness of Equilibrium Parameters of Adhesion in Predicting the Outcome of Competition for Bacterial Receptor Sites on Respiratory Epithelial Cells byPseudomonas aeruginosaStrains of Heterologous Pilus Type

The adhesion of Pseudomonas aeruginosa strain O(PAO) to human buccal epithelial cells (BECs) was analysed by an equilibrium analysis of binding and the equilibrium parameters of adhesion determined. PAO bound to a maximum of 159±28 receptor sites per BEC with an apparent association constant (Ka) of 2.89(± 1.76) ± 10−8 ml/CFU. As P.aeruginosa strain K(PAK) employs pili to adhere to BECs and there is substantial homology between the PAK pilin gene and the PAO pilin gene, the potential for competition for receptor sites on the BEC surface was investigated. PAO and PAK competed for receptor sites in a reciprocal manner, although PAO was ∼ 10 fold more effective in competing for receptor sites than was PAK. Purified pili inhibited the adhesion of the heterologous strain, PAO pili being ∼ 10 fold more effective than PAK pili in this heterologous inhibition. The difference in effectiveness of PAO and PAO pili in competing with PAK and PAK pili for receptor sites reflected the difference in the Kas of the two strains.