STRUCTURAL AND ANTIGENIC TYPES OF CELL-WALL POLYSACCHARIDES FROM VIRIDANS GROUP STREPTOCOCCI WITH RECEPTORS FOR ORAL ACTINOMYCES AND STREPTOCOCCAL LECTINS

Lectin-mediated interactions between oral viridans group streptococci and actinomyces may play an important role in microbial colonization o f the tooth surface. The presence of two host-like motifs, either GalN Ac beta 1-->3Gal (Gn) or Gal beta 1-->3GalNAc (G), in the cell wall po lysaccharides of five streptococcal strains accounts for the lactose-s ensitive coaggregations of these bacteria with Actinomyces naeslundii. Three streptococcal strains which have Gn-containing polysaccharides also participate in GalNAc-sensitive coaggregations with strains of St reptococcus gordonii and S. sanguis, Each Gn-or G-containing polysacch aride is composed of a distinct phosphodiester-linked hexa-or heptasac charide repeating unit. The occurrence of these polysaccharides on 19 additional viridans group streptococcal strains that participate in la ctose-sensitive coaggregations with actinomyces was examined, Negative ly charged polysaccharides that reacted with Bauhinia purpurea aggluti nin, a Gal and GalNAc binding plant lectin, were isolated from 17 stra ins by anion exchange column chromatography of mutanolysin-cell wall d igests. Results from nuclear magnetic resonance and immunodiffusion id entified each of 16 polysaccharides as a known Gn-or G-containing stru ctural type and one polysaccharide as a new but closely related Gn-con taining type. Unlike the reactions of lectins, the cross-reactions of most rabbit antisera with these polysaccharides were correlated with s tructural features other than the host-like motifs. Gn-containing poly saccharides occurred primarily on the strains of S. sanguis and S. ora lis while G-containing polysaccharides were more common among the stra ins of S. gordonii and S. mitis examined. The findings strongly suppor t the hypothesis that lectin-mediated recognition of these streptococc i by other oral bacteria depends on a family of antigenically diverse Gn-and G-containing cell wall polysaccharides, the occurrence of which may differ between streptococcal species.