Surface free energies of oral streptococci and their adhesion to solids

Abstract The adhesion of 3 strains of oral streptococci from a buffered suspension onto 3 different solid substrata was studied. Representative strains of streptococci were selected on the basis of their surface free energy ( γ _b), namely Streptococcus mitis L1 ( γ _b= 37 mJ·m^?2), Streptococcus sanguis CH3 (95 mJ·m^?2) and Streptococcus mutans NS (117 mJ·m^?2). Solid substrata were also selected on basis of their surface free energy ( γ _s), and included polytetrafluorethylene ( γ _s= 20 mJ·m^?2), polymethylmethacrylate (53 mJ·m^?2) and glass (109 mJ·m^?2). Bacterial adhesion was measured as the number of bacteria adhering per cm² at equilibrium. Equilibrium was usually obtained within 20 min. S. sanguis CH3, having an intermediate surface free energy did not show a clear preference for any of the 3 solids. S. mitis L1, however, the lowest surface free energy strain, adhered in highest numbers to the low energy solid PTFE, whereas the highest γ _b strain, S. mutans NS, adhered in highest numbers to the highest γ _s solid, glass. Calculation of the interfacial free energy of adhesion ( ΔF _adh) for each bacterial strain showed that this parameter was predictive of bacterial adhesion to solid substrata.