Kinetics of adhesion of the oral bacterium Streptococcus sanguis CH3 to polymers with different surface free energies

Abstract

The kinetics of adhesion of Streptococcus sanguis CH3 from suspension to polymers with different surface free energies were studied by using three bacterial concentrations (2.5 x 107, 2.5 x 108, and 2.5 x 109 cells per ml-1). Substratum surface free energies (γ(s)) ranged from 18 to 120 erg cm-2. The kinetics of bacterial adhesion to these surfaces showed a typical two-step adhesion process, indicating an equilibrium in both steps. In the initial adhesion step (step 1), low equilibrium numbers of adhering bacteria were counted on substrata with surface free energies lower than 55 erg cm-2. A maximal number adhered on substrata with higher surface free energies. At the lowest bacterial concentration tested, the highest number of bacteria were found on substrata with a surface free energy around 55 erg cm-2. For each substratum, step 2 started after a characteristic time interval τ* being short (30 min) for γ(s) < 50 and long (120 min) for γ(s) > 50 erg cm-2. The relationship between the substratum surface free energy and the number of bacteria adhering at equilibrium after step 2 was similar to, although less distinct than, that during step 1 with a slight indication of a bioadhesive minimum around γ(s) = 35 erg cm-2. The results are indicative of a two-step adhesion model, in which step 1 is controlled by macroscopic substratum properties.