Bacterial adhesion onto apatite minerals —electrokinetic aspects

The role of the electrokinetic properties of Streptococcus sanguis and Actinomyces naeslundii in determining their adhesion to apatite minerals is examined. It is shown that bacterial adhesion onto a mineral surface takes place even when both the surfaces are negatively charged, and that the adhered layer is resistant to washing. Also, the mineral fines after exposure to bacteria exhibit zeta potential values which are in between those of the mineral and the bacteria, but lie closer to that of the mineral. In the absence of salivary proteins, the inorganic species present in saliva alter the magnitude of the surface charge but do not affect the bacterial adhesion process. Dissolved apatite mineral species (in supernatant solutions) are also shown to decrease the magnitude of the zeta potential of the bacteria. The observed adsorption of negatively charged bacteria onto negatively charged minerals suggests that electrostatic interactions are not the primary factors determining adhesion.