Saliva-mediated binding in vitro and prevalence in vivo of Streptococcus mutans

The contention that the colonization of oral tissues requires the adhesion of bacteria is undisputed, but adherence can only be studied quantitatively in vitro. It has never been seriously challenged whether the adherence phenomena measured in vitro reflect differences in levels of in vivo colonization. The objective of this study was to investigate the adherence-promoting ability of saliva from persons harbouring Strep. mutans in the range from non-detectable levels to more than 106 colony-forming units/ml. Saliva-mediated adherence of Strep. mutans is promoted by high molecular-weight glycoproteins, agglutinins, which also causes aggregation of the bacteria. Adherence and aggregation of Strep. mutans was investigated individually using parotid saliva from 41 persons. Heavily colonized individuals did not promote adherence better than those with relatively few indigenous bacteria. Aggregation was found to be less rapid with parotid saliva from the heavily colonized individuals (p < 0.05). The results indicate that parotid saliva primarily affects the in vivo prevalence of Strep. mutans by clearing the bacteria from the mouth rather than promoting adherence.