Inhibition of Streptococcus mutans Adherence to Hydroxyapatite with Combinations of Alkyl Phosphates and Nonionic Surfactants

Seven alkyl phosphate derivatives and three nonionic surfactants were examined for their ability to inhibit the adherence of 3H-labelled cells of Streptococcus mutans to hydroxyapatite (HA) treated with buffer (BHA) or parotid saliva (SHA). None of the compounds alone hindered binding of bacteria to BHA or SHA effectively. A combination of certain of the alkyl phosphates, notably a disodium phosphate of 1-octadecanol, and nonionic surfactant at a 1:1 molar ratio gave a strong inhibition of S. mutans adherence. Treatment of SHA with this combination resulted in 98% reduction of adherence. Adsorption of the two types of surface-active agents alone and in combinations was studied using 14C-labelled agents. Electrophoretic measurements revealed that surfaces treated with only alkyl phosphate became highly negatively charged, while surfaces treated with the combination had a zeta-potential of around zero. The results suggest that treatment with surfactants might be used to interfere with bacterial adherence on the tooth surface.