Bacteria-agglutinating glycoproteins in human saliva : an in vitro study with special reference to Streptococcus mutans

Abstract: The activity and specificity of salivary glycoproteins (agglutinins) aggregating various human indigenous microorganisms were studied in vitro. The agglutinin reacting with a serotype c strain of Streptococcus mutans was isolated and chemically characterized.The results can be summarized as follows:1. Saliva contains agglutinins against predominant oral microorganisms but also against some of the predominant intestinal bacteria. Agglutinin from one individual was active against microorganisms both from this individual and other individuals.2. Saliva-induced agglutination of S. sanguis was inhibited by antisera to IgA, IgG, IgM, and secretory component while S. mutans agglutination was inhibited only by albumin and antisera to IgA. The differences in inhibition indicate the presence of different agglutinins for the two strains.3. The agglutinin for an S. mutans serotype c strain was sensitive to a reduction in pH and to treatment with Concanavalin A while an S. mitior agglutinin was not. The tested S. mitior strain, however, adsorbed the S. mutans agglutinin without being agglutinated.4. The agglutinin reacting with an S. mutans serotype c strain could be desorbed from the microorganisms in a neutral phosphate buffer. Calcium in the order of 10 million molecules per bacteria was needed to restore agglutination induced by the isolated agglutinin.5. The agglutinin in parotid saliva responsible for aggregation of an S. mutans serotype c strain was characterized as a non-immunoglobulin glycoprotein with no blood group activity. The agglutinin was a polymer with a molecular weight exceeding 5 000 kdaltons while the monomeric agglutinin had a molecular weight of 440 kdaltons. The concentration of the agglutinin in parotid saliva was as low as 0.5 per cent of total protein but because 0.1 ug of the agglutinin caused rapid aggregation of as many as 100 million bacteria the agglutinin is considered highly active.The results indicate the presence in saliva of different agglutinins with specificity for different bacterial species. High molecular weight glycoproteins seem to play a major role in saliva-induced agglutination of microorganisms and in mechanisms related to clearance and retention of oral microorganisms.