Surface free energies of oral streptococci

The surface free energies (γb) of a variety of oral streptococci were determined from contact angle measurements on bacterial deposits, using the concept of dispersion and polar components. At least four strains of each species were tested. Strains of Streptococcus mutans, S. sanguis and S. salivarius possessed relatively high surface free energies (103 ± 12 mJ · m−2) and at the species level no significant difference was found. In contrast, the strains of S. mitis had remarkably low surface free energies (45 ± 14 mJ · m−2). S. milleri appeared to be a heterogeneous species, showing surface free energies over a range of 32–119 mJ · m−2. No significant differences were observed between laboratory strains and strains freshly isolated from the oral cavity.