Ultrastructural visualization of the adherence of Streptococcus mutans and Streptococcus salivarius to hydroxyapatite

S. mutans and S. salivarius adherence to saliva-coated and saliva-uncoated hydroxyapatite was studied by transmission and high resolution scanning electron microscopy. No difference was observed between the saliva-coated and saliva-uncoated study series of adherence. The attachment of individual bacteria to apatite crystals was found to be mediated by cell wall projections. These electron-dense structures were characteristically well formed in S. mutans, and even in S. salivarius the projections appeared to link the bacteria to the apatite. The site of attachment in the bacterial cell wall was always at the division area. We suggest that the possible metabolic activity at the cell wall division site, therefore, also works in the adherence process.