Effect of pH and counter ions on the zeta-potential of oral streptococci

Abstract

The ζ-potentials of 10 different strains of Streptococcus mutans, Streptococcus sanguis and Streptococcus salivarius were determined in the pH range 2.5–8.0 and after incorporation of counter ions in the running media, using a standardized particle microelectrophoretic technique. The results indicate that the surface potentials of oral streptococci are pH-dependent and that this dependence is related to the microbial strain. The effects are probably caused by presence of different kinds as well as different amounts of charged groups on the bacterial surfaces. Anions did not have noticeable influence on the ζ-potential of the microorganisms but multivalent cations decreased it. Some of these were even able to change the potential of the streptococci to positive. Generally speaking, the variations of the ζ-potentials were in accord with accepted colloid and surface chemical laws and phenomena.