Aggregation of group A streptococci by human saliva and effect of saliva on streptococcal adherence to host cells

Abstract

The aggregation of group A streptococci by whole, stimulated human saliva (WHS) and the effect of saliva on streptococcal adherence to host cells was investigated. WHS samples from 11 individuals were found to aggregate both M+ and M- group A streptococci to various degrees. The aggregating activity was sensitive to heat, EDTA, EGTA [ethylene glycol-bis(β-aminoethyl ether)-N,N,N',N'-tetraacetic acid], sodium dodecyl sulfate, and lipoteichoic acid. None of the simple sugars tested, mercaptoethanol, albumin, or nonionic detergents had any effect on aggregation. The aggregating activity of EDTA-treated saliva was restored by 0.1 mM Ca2+ and 1.0 mM Mn2+ but not by up to 5 mM Mg2+. Only streptococci from the stationary phase were aggregated. Hyaluronidase treatment of streptococci from the exponential phase of growth restored their ability to be aggregated, suggesting that the hyaluronic acid capsule interferes with agglutination. Adsorption of WHS by one strain of Streptococcus pyogenes removed aggregating activity for other strains of S. pyogenes and Streptococcus sanguis but not agglutinins for Escherichia coli, suggesting that the agglutinin is specific for certain gram-positive bacteria. Molecular sieve chromatography of WHS and identification of streptococcus-binding components of saliva suggest that either a glycoprotein of ~360 kDa or a mucin of saliva of >1,000 kDa mediates aggregation of streptococci. WHS also inhibited adherence of S. pyogenes to buccal epithelial cells.