Reversibility of adhesion of oral streptococci to solids

Abstract

The reversibility of adhesion of 3 representative strains of oral streptococci from a phosphate-buffered suspension onto 5 different solid substrata was studied. Streptococcus mitis T9 (surface free energy γb= 39 mJ · m−2). Streptococcus sanguis CH3 (γb= 95 mJ · m−2) and Streptococcus mutans NS (γb= 117 mJ · m−2) were selected on basis of their surface free energy. Solid substrata were employed with a surface free energy γs ranging from 20 mJ · m−2 for polytetrafluorethylene to 109 mJ · m−2 for glass. Bacterial suspensions containing 2.5 × 109 cells per ml were incubated with 2 samples of each substratum. After 1 h the number of adhering bacteria was evaluated on one sample, while the second sample was kept for another hour at a 10-fold lower bacterial concentration. Bacteria with a low surface free energy desorbed only from substrata with a high surface free energy, while bacteria with a high surface free energy desorbed from substrata with a low surface free energy. Thus low energy bacterial strains adhered reversibly to high energy substrata and vice versa. Similar observations were made with polystyrene particles. Calculation of the interfacial free energy of adhesion (ΔFadh) for each bacterial strain as well as for the polystyrene particles showed that a reversible adhesion was associated with a positive ΔFadh, denoting unfavourable adhesion conditions upon a thermodynamic basis.