Role of sialic acid in saliva-induced aggregation of Streptococcus sanguis.

The ability of saliva to induce aggregation of Streptococcus sanguis was destroyed by treating the saliva with protease or neuraminidase. Loss of aggregating activity could be correlated with the appearance of free sialic acid. Clarified saliva contains an endogenous neuraminidase that modifies aggregating activity. Aggregation was inhibited by mixed ganglioside preparations but less effectively by acid-hydrolyzed gangliosides. The aggregating activity of S. sanguis was not related to the rhamnose or phosphorous content of the cell wall or to antigen a, b, c, d, or e.