Physico-chemical properties of oral streptococcal cell surfaces and their relation with adhesion to solid substrata in vitro and in vivo

Abstract

Thermodynamic approaches to bacterial adhesion emphasizing macroscopic properties of interacting bacterial cell and solid substratum surfaces are often criticized for not sufficiently accounting for microscopic, stereochemically complementary molecular interactions between the surfaces. Yet, as is demonstrated in this paper for a set of oral streptococci, three completely different overall macroscopic bacterial cell surface properties (elemental composition by XPS, surface free energy by contact angles and isoelectric point) are related in a comprehensible way, even though bacteria are analyzed at different states of hydration. Moreover, streptococcal adhesion from a moderate flow (σ=21 s −1)to inert solid substrata was related to both the interfacial free energy of adhesion and a strain-dependent microbial factor. This empirical factor measures the effect of cell surface appendages or excretion of (anti-) adhesives which assist or impede adhesion in excess of strictly thermodynamic considerations. Although bacterial adhesion strongly decreased after precoating substrata with bovine serum albumin or salivary proteins, negative slopes between the number of adhering streptococci and the interfacial free energy of adhesion (calculated on basis of the bare solid substratum surface free energies) suggest that surface free energy effects are transferred through adsorbed protein films. Much stronger evidence for such modification of adsorbed protein films by substratum surface free energies is obtained from in vivo experiments in the human oral cavity which demonstrated that the amount of plaque collected on various materials after nine days exposure to oral fluids was approximately five times smaller on a low surface free energy material as PTFE-teflon than on a high surface free energy material such as enamel.