Aggregation of Streptococcus sanguis by a neuraminidase-sensitive component of serum and crevicular fluid.

A number of strains of Streptococcus sanguis were found to aggregate in nonimmune serum and in crevicular fluid. All strains which aggregated in serum also aggregated in saliva, but some strains which aggregated in saliva did not aggregate in serum. Aggregation was destroyed by treatment of serum or crevicular fluid with neuraminidase and was inhibited by gangliosides. Treatment of serum with proteases reduced aggregating activity. Adsorption of serum to hydroxyapatite did not reduce the aggregating activity. The aggregating factor was partially purified by gel filtration and polyacrylamide gel electrophoresis and was found to be an acidic glycoprotein with a molecular weight of greater than 200,000, comprised of subunits with molecular weights of approximately 100,000. It did not appear to be an immunoglobulin and could not be identified with any other serum component tested. The possible role of the aggregating factor in providing nonimmune protection against colonization of S. sanguis in the gingival crevice and blood is discussed.     

Optimization of an hydroxyapatite adhesion assay for Streptococcus sanguis

Previous studies have compared the adhesion of [3H]thymidine-labeled Streptococcus sanguis to saliva-coated hydroxyapatite (SHA) and buffer-coated hydroxyapatite (HA) beads. Although the hypotonic buffer used in these assays was adjusted to simulate saliva, it does not necessarily provide the optimal parameters for the quantitative estimate of adhesion under in vitro conditions. Optimization is necessary to provide the maximum sensitivity of the assay for detecting the effects of various salivas as well as for quantitating the effect of environmental growth conditions on the adhesion of S. sanguis to SHA and HA. A major distinction between the adhesion of S. sanguis to SHA and HA was observed when the bacterial concentration was varied. At high cell concentrations, the number of cells adhering to SHA was twice the number adhering to HA. Such differences were not detected at low cell concentrations. The optimal pH for the adsorption to both SHA and HA was 6. Changes in the ionic strength or addition of mono- or divalent cations found in saliva had little effect on adhesion to HA. In contrast, high concentrations of monovalent cations inhibited adhesion to SHA. Anions such as carbonate, chloride, and sulfate did not have specific effects on adhesion, whereas acetate inhibited adhesion to both SHA and HA. Fluoride inhibited adhesion to both SHA and HA, suggesting an interaction between fluoride and hydroxyapatite. These results indicated that 2 mM phosphate buffer at a pH of 6 containing 5 mM KCl and 1 mM CaCl2 was the optimal buffer for studying the in vitro adhesion of S. sanguis to SHA.     

Recombination-deficient Streptococcus sanguis.

A UV-sensitive derivative was obtained from Streptococcus sanguis Challis. The organism could be transformed with a number of small streptococcal plasmids at frequencies equal to, or 1 logarithm below, the transformation frequencies for the parent organism. However, transformation with chromosomal DNA was greatly impaired in the UV-sensitive derivative.     

Characterization of an adhesion antigen of Streptococcus sanguis G9B.

An antigen possessing the attributes of an adhesion has been identified in Streptococcus sanguis G9B. Cell surface components were extracted from G9B and a spontaneously occurring nonadherent mutant of G9B, strain Adh-, with a 2 mM barbital buffer, pH 8.6. The extract of G9B but not of Adh- absorbed more than 80% of the adhesion-inhibitory activity of anti-G9B immunoglobulin G (IgG). Immunoblots revealed 80- and 52-kilodalton (kDa) antigens present in the G9B extract but not in the Adh- extract. Absorption of anti-G9B IgG with Adh- and G9B barbital extracts showed a correlation between the loss of the 80- and 52-kDa antibodies and the loss of adhesion-inhibitory activity. An antibody prepared against the 80-kDa antigen excised from sodium dodecyl sulfate-polyacrylamide gels recognized the 80- and 52-kDa antigens and another antigen of 62 kDa but did not inhibit adhesion. However, an antibody from an electroblot containing the native protein from which the 80-kDa and related antigens were derived (the 80-kDa antigen complex) inhibited adhesion to the same extent as anti-G9B IgG. Periodate oxidation of the G9B barbital extract modified the 80-kDa antigen complex and resulted in the loss of 40% of its absorbing activity. The barbital extract also contained an endogenous enzyme responsible for producing the 62- and 52-kDa antigens from the 80-kDa protein and which, under optimal conditions, degraded the antigen completely, resulting in the loss of antibody-absorbing activity. The 80-kDa antigen complex has a molecular mass of more than 200 kDa in native polyacrylamide gels and a pI of 4.1 to 4.8. These observations suggest that the adhesion antigen in S. sanguis G9B is a large glycoprotein from which an 80-kDa antigen complex is derived.     

Comparison of Streptococcus mutans and Streptococcus sanguis receptors for human salivary agglutinin.

Oral streptococci vary in their susceptibility to salivary agglutinin-mediated aggregation. To understand the molecular basis of this specificity, the structure and function of receptors for agglutinin from Streptococcus mutans KPSK2 (MSL-1) and Streptococcus sanguis M5 (SSP-5) were compared. Immunological screening of an S. mutans KPSK2 genomic DNA library yielded two identical clones expressing a streptococcal protein that co-migrated with a 220 kDa peptide in SDS extracts from this organism. This protein inhibited agglutinin-mediated aggregation of S. mutans KPSK2 in a dose-dependent manner. The MSL-1 gene is homologous to the S. mutans SpaP and pac genes although single base substitutions alter several amino acids. MSL-1 is also similar to the agglutinin receptor (SSP-5) cloned from S. sanguis M5. All three proteins, MSL-1, P1, and SSP-5 share at least one epitope since monoclonal and polyclonal anti-SSP-5 antibodies react with both MSL-1 and P1. However, other monoclonal antibodies are specific for SSP-5 and appear to react with a peptide domain exhibiting little homology to MSL-1 or P1. Sugar inhibition studies showed that agglutinin-mediated aggregation of S. mutans KPSK2 was most potently inhibited by fucose and lactose. Sialic acid, a potent inhibitor of S. sanguis aggregation, had no effect on the interaction of agglutinin with S. mutans KPSK2. These results suggest that while the MSL-1 and SSP-5 proteins are genetically and immunologically related, their specificity for binding sites on agglutinin differs.     

Aggregation and Adherence of Streptococcus sanguis: Role of Human Salivary Immunoglobulin A

Fourteen freshly isolated strains of Streptococcus sanguis were obtained from the dental plaque of five healthy adults. Whole saliva was collected concomitant with the plaque isolates from the five subjects, and a second whole saliva sample was collected 10 weeks later. All possible combinations of the first five saliva samples, the second five saliva samples, and 14 strains of bacteria were tested for aggregation. Of the 140 combinations examined, 108 of 140 (77%) of the strains aggregated with the first saliva samples and 95 of 140 (68%) aggregated with the second saliva samples. Overall, 72% of the strains aggregated with both the first and second saliva samples. Removal of immunoglobulin A (IgA) from these same salivas resulted in 38 of 108 (35%) of the aggregates decreasing in intensity with the first saliva samples and 27 of 95 (29%) of the aggregates decreasing in intensity with the second saliva samples. No aggregates increased in intensity with saliva samples when IgA had been removed. Removal of IgA from saliva also resulted in a mean decrease of 46% in adherence of S. sanguis to hydroxyapatite coated with the IgA-deficient saliva. Several strains of S. sanguis were shown to aggregate strongly with human salivary and colostral IgA. In addition, S. sanguis strain S7 showed a 31% stimulation of adherence to hydroxyapatite precoated with human salivary IgA over the uncoated controls. Stepwise removal of IgA from saliva resulted in a decrease in aggregation intensity from strong (4+) to weak (1+ to 2+). Similarly, the adherence of S. sanguis to hydroxyapatite coated with these saliva samples decreased linearly as the salivary IgA was depleted. Alternatively, the addition of a small quantity of salivary IgA (20 mug/ml) to progressively diluted saliva maintained a high level of adherence and strong aggregation until the saliva dilutions reached between 1:8 in the adherence experiments and 1:32 for the aggregations. These data indicate that salivary IgA may play an important role in the microbial ecology of human dental plaque formation.     

Antibodies that bind to fimbriae block adhesion of Streptococcus sanguis to saliva-coated hydroxyapatite.

Antibodies raised against a fimbriated, adhesive strain of Streptococcus sanguis (FW213) were found to block the adhesion of this organism to saliva-coated hydroxyapatite. Antibodies were made specific for adhesion antigens by adsorption with isogenic, nonadhesive mutants (for rabbit polyclonal adsorbed antibody) or selection based on nonreactivity with two nonadhesive mutants (for monoclonal antibody). Rabbit antibody raised against isogenic, nonfimbriated nonadhesive mutants served as a control for antibodies present, but not related to fimbriation. Adsorbed antibody and monoclonal antibody were shown to be specific for fimbriae (antigen 1), since both antibodies could be seen by immune electron microscopy to bind 3.6-nm fimbriae, reacted only with the fimbriated parent and not the mutants in a whole bacterial cell enzyme-linked immunosorbent assay, and could immunoprecipitate fimbriae from fimbrial extracts of FW213. Antibodies isolated from preimmune and mutant sera did not react with fimbriae in any of the above assays. Only adsorbed antibody and monoclonal antibody were capable of blocking the adhesion of FW213 to saliva-coated hydroxyapatite. Adsorbed antibody, purified to immunoglobulin G (IgG), was an effective inhibitor of adhesion without causing interfering cellular aggregation. Monoclonal IgG, papain-cleaved to Fab fragments to prohibit cell-to-cell cross-linking, was also a potent inhibitor of S. sanguis FW213 adhesion. Both IgG from mutant sera and Fab fragments from normal mouse IgG could not be shown to block adhesion. These data further support the hypothesis that S. sanguis fimbriae are involved in adhesion.     

Role of sialic acid in the kinetics of Streptococcus sanguis adhesion to artificial pellicle.

Evaluation of the kinetics of adhesion of Streptococcus sanguis 10556 to saliva-coated hydroxylapatite revealed that sialic acid played a role in the formation of a stable cell-substratum complex. In a previous paper (M. M. Cowan, K. G. Taylor, and R. J. Doyle, J. Dent. Res. 65:1278-1283, 1986) the adhesion was found to take place in two distinct stages: a reversible equilibrium, probably governed by long-range forces, followed by a transition to higher-affinity binding. In the present study, artificial pellicle was treated with neuraminidase, and kinetic adsorption and desorption experiments with S. sanguis were conducted. The depletion of sialic acid from pellicle decreased the initial adsorption rate constant only slightly. The rate constant describing the initial desorption was unaffected. However, no transition to the second (high-affinity) association occurred. While S. sanguis desorption from control pellicles exhibited two sequential rates, with the second rate being approximately 10 times slower than the first, all desorption from sialo-deficient pellicles occurred at one rate that was equivalent to the initial rate constant for control desorption. The cells did not reach an equilibrium with the sialo-deficient pellicle, even after 6 h. Competing sialic acid did not decrease the rate or extent of adsorption, but desorption occurred to a greater extent when cells had adsorbed in the presence of sialic acid. These data suggest that sialic acid plays little role in the initial association of cell and pellicle but that it is necessary for the transition to high-affinity binding and the concomitant decreased propensity to desorb.     

Antigens of Streptococcus sanguis

An antigenic analysis of the alpha-hemolytic streptococci isolated from dental plaque was performed by use of antisera against a strain of Streptococcus sanguis (M-5) which was isolated from dental plaque. Immunoelectrophoretic and Ouchterlony tests of Rantz and Randall extracts of 45 strains gave positive reactions with the M-5 antisera. These strains represented 60% of the strains tested. The number of antigens which could be identified in these extracts varied from one to five and were designated a to e. The a antigen was found in 36 of the strains tested, including reference strains of S. sanguis and the group H streptococci. The strains reacting with the M-5 antisera were divided into two majors types: type I consisted of 23 strains in which the a antigen was found alone or with one or more of the c, d, and e antigens; type II consisted of 13 strains in which both the a and b antigens were found with or without one or more of the c, d, and e antigens. The remaining strains contained, either singly or in combination, the b, c, d, and e antigens but not the a antigen. Biochemical tests of representatives of each serotype and reference strains indicated that strains reacting with M-5 antisera were S. sanguis. These findings suggest that S. sanguis strains share common physiological and serological properties.     

Aggregation of human blood platelets by vasopressin

Synthetic [8-arginine]-vasopressin, [8-lysine]-vasopressin, [8-ornithine]-vasopressin or [2-phenylalanine, 8-lysine]-vasopressin aggregated human platelets in heparinized platelet-rich plasma. The lowest effective concentrations (1-4mU/ml) caused a primary transient aggregation, while higher concentrations also caused a secondary irreversible aggregation. Vasopressin was almost inactive in citrated platelet-rich plasma but caused aggregation in recalcified citrated or native material. Vasopressin also aggregated washed human platelets suspended in buffered saline, if fibrinogen and either Ca2+ or Mg2+ ions were present. Ethylene glycol-bis (beta-aminoethyl ether)-N,N'-tetraacetic acid inhibited aggregation completely but only after preincubation with the platelets, suggesting that platelet-bound calcium was also required. Phosphocreatine with creatine phosphokinase partially inhibited primary aggregation of platelets by vasopressin and prevented secondary aggregation, which suggests that release of platelet ADP contributed to these processes. Concentrations of vasopressin causing irreversible aggregation released small amounts of 14C from platelets containing serotonin-14C. Platelet aggregation induced by vasopressin was inhibited by adenosine, prostaglandin E1, N6,2'-0-dibutyryl cyclic 3',5'-AMP, caffeine, imipramine, or N-ethylmaleimide. Adenosine and prostaglandin E each inhibited the action of vasopressin much more powerfully than that of ADP and, therefore, cannot act solely by inhibiting the effects of the ADP released. In several respects the effect of vasopressin on blood platelets resembled its action on smooth muscle.     

Cell-free released components of Streptococcus sanguis inhibit human platelet aggregation

To study the role of surface components in the selective binding and aggregation of platelet-rich plasma (PRP) by strains of viridans streptococci, we treated the binding, aggregation strain Streptococcus sanguis I 2017-78 by sonication or trypsinization. Morphologically identifiable electron-dense fibrils were released from the cell wall, apparently from an inner electron-dense layer, under conditions that left cells intact. These controlled conditions were determined to cause submaximal loss in adhesion to platelet ghosts and PRP aggregation by treated, washed S. sanguis. Soluble components were recovered from the controlled sonic or L-(tosylamido 2-phenyl)ethyl chloromethyl ketone-trypsin treatments. Each showed dose-response inhibition of aggregation when preincubated with PRP before challenge with fresh, untreated S. sanguis. The time to onset of PRP aggregation was inhibited by 50% with 0.2 mg of TPCK-trypsin peptides or 1.0 mg of the sonicate per ml per 2 X 10(8) platelets. Components of both preparations were immunologically cross-reactive, but lipoteichoic acid was not a major antigen of either. By weight, the TPCK-trypsin peptides were virtually all protein; the sonicate residues identified were about 50% protein and 7% hexose. Each was a complex mixture of components as shown by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. More than 8 TPCK-trypsin peptides and 16 sonicate components were so identified. In contrast, at least four or five components from either preparation were recognized as surface determinants by a rabbit antiserum to whole homologous microbes. Platelet-binding ligands of S. sanguis could be among these determinants.     

Lactose-reversible coaggregation between oral actinomycetes and Streptococcus sanguis.

Freshly isolated strains of oral actinomycetes were obtained from human dental plaque and were tested for the ability to coaggregate with common laboratory stock strains of Streptococcus sanguis. Strains belonging to the genera Actinomyces, Arachnia, Bifidobacterium, and Bacterionema were isolated. Only members of the genus Actinomyces coaggregated with the streptococci, and only Actinomyces viscosus and Actinomyces naeslundii exhibited lactose-reversible interactions. A total of 61 strains, consisting of all of the A. viscosus isolates and 86% of the A. naeslundii isolates, coaggregated; 87% inhibited lactose-reversible coaggregation. On the basis of this property and the altered ability of strains to coaggregate after heat treatment of the cells, we delineated four coaggregation groups. The other 13% of the strains constituted a fifth group, which was characterized by a pattern of closely related interactions that were not reversed by lactose. Compared with previously characterized coaggregation properties determined with stock culture strains of actinomycetes, more than 80% of these fresh isolates exhibited identical coaggregation properties. Thus, most of the coaggregation between freshly isolated oral actinomycetes and streptococci involves lactose-reversible cell-cell interactions, which suggests that such coaggregation is mediated by a network of lectin-carbohydrate interactions between complementary cell surface structures on the two cell types.     

Corncob formation between Fusobacterium nucleatum and Streptococcus sanguis.

Corncob formation in dental plaque was believed to be limited to strains of Bacterionema matruchotii and Streptococcus sanguis. We observed recently that strains of Fusobacterium nucleatum also interacted with S. sanguis to form corncobs. Since the fusobacteria are among the first anaerobic filaments to colonize subgingival plaque, these interactions could serve as a connecting link between the transformation of supra- to subgingival plaque. To further characterize these interactions, quantitative in vitro studies of the kinetics of corncob formation of the fusobacteria were undertaken. These studies indicated that fewer streptococci were needed to saturate F. nucleatum strain 364 compared to strain 10953. Corncob formation with both strains was enhanced with increasing pH up to pH 8, at which point autoaggregation of the streptococci occurred. Variation in ionic strength and divalent cations had little effect on the interaction, and EDTA suppressed aggregate formation only slightly. Detergents at concentrations above 0.05% also inhibited corncob formation. Electron micrographs suggested that attachment of the cocci to the fusiforms was mediated through localized tufts of fimbriae, as they are in the Bacterionema system. However, although both trypsin and heat treatment of the streptococci inhibited corncob formation with fusobacteria, the effects were not as complete as those seen in Bacterionema species. Unlike the Bacterionema model, trypsin and heat treatment of the fusobacteria resulted in inhibition of corncob formation. These results suggest that several different receptors may be involved in corncob formation.     

Immunoelectron microscopic identification and localization of Streptococcus sanguis with peroxidase-labeled antibody: localization of Streptococcus sanguis in intact dental plaque.

Streptococcus sanguis has been localized ultrastructurally within intact dental plaque by means of an indirect technique which utilizes horseradish peroxidase-labeled antibody. The technique allows for complete diffusion of the reagents to all portions of the plaque specimens. Control procedures can be carried out on serial sections of plaque with a bacterial composition similar to that of the experimental specimen. The 30-mum-thick sections can be examined in the light microscope to localize areas specifically labeled with peroxidase prior to cutting ultra-thin sections for electron microscopy. This study demonstrated that specific bacteria can be localized within intact dental plaque. The results also indicated that S. sanguis grows in dental plaque as columnar shaped microcolonies perpendicular to the tooth surfaces. Growth appears to be by cell division rather than deposition of new cells at the surfaces. Despite their relatively good structural preservation, the cells in the deeper (older) layers of plaque appear to have lost some of their antigenic activity in comparison to the cells near the surface.     

Role of granulocytes in experimental Streptococcus sanguis endocarditis.

We investigated the role of granulocytes during the induction and course of experimental Streptococcus sanguis endocarditis in rabbits by depleting blood granulocytes with nitrogen mustard. The induction of the endocarditis was not influenced by granulocytopenia: the 50% infectious dose was 5.4 X 10(4) colony-forming units in normal and granulocytopenic rabbits. However, granulocytopenia influenced the curse of the endocarditis, as shown by a significant increase in the number of colony-forming units per gram of vegetation (P less than 0.02) from 24 to 72 h after the injection of 10(5) colony-forming units of S. sanguis. This rise did not occur in the control rabbits. Furthermore, bacteremia was significantly higher in the granulocytopenic rabbits (P less than 0.05) during the first 48 h compared with the control rabbits. This was not because of altered clearance of the streptococcus inoculum or seeding of streptococci from extracardiac bacterial foci. We concluded that granulocytes have no measurable effect on the induction of S. sanguis endocarditis, but during the course of the endocarditis, granulocytes keep the endocardial infection in check.     

Characterization of salivary alpha-amylase binding to Streptococcus sanguis.

The purpose of this study was to identify the major salivary components which interact with oral bacteria and to determine the mechanism(s) responsible for their binding to the bacterial surface. Strains of Streptococcus sanguis, Streptococcus mitis, Streptococcus mutans, and Actinomyces viscosus were incubated for 2 h in freshly collected human submandibular-sublingual saliva (HSMSL) or parotid saliva (HPS), and bound salivary components were eluted with 2% sodium dodecyl sulfate. By sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western transfer, alpha-amylase (EC 3.2.1.1) was the prominent salivary component eluted from S. sanguis. Studies with 125I-labeled HSMSL or 125I-labeled HPS also demonstrated a component with an electrophoretic mobility identical to that of alpha-amylase which bound to S. sanguis. Purified alpha-amylase from human parotid saliva was radiolabeled and found to bind to strains of S. sanguis genotypes 1 and 3 and S. mitis genotype 2, but not to strains of other species of oral bacteria. Binding of [125I]alpha-amylase to streptococci was saturable, calcium independent, and inhibitable by excess unlabeled alpha-amylases from a variety of sources, but not by secretory immunoglobulin A and the proline-rich glycoprotein from HPS. Reduced and alkylated alpha-amylase lost enzymatic and bacterial binding activities. Binding was inhibited by incubation with maltotriose, maltooligosaccharides, limit dextrins, and starch.     

Expression of Streptococcus sanguis antigens in Escherichia coli: cloning of a structural gene for adhesion fimbriae.

Chromosomal DNA from Streptococcus sanguis FW213 was partially digested with EcoRI and ligated into the positive-selection cloning vector pOP203(A2+). The ligation mixture was used to transform Escherichia coli K-12, and 4,500 transformants were examined. The tetracycline-resistant colonies had inserts averaging 3.2 kilobases. The entire colony bank was screened by colony immunoassay with polyclonal rabbit serum raised against S. sanguis FW213 whole cells. Thirty recombinant colonies produced stable positive reactions of various intensities, indicating that S. sanguis antigens could be expressed in E. coli. Restriction endonuclease digestion of these clones suggested that 26 of the clones were unique. Only two clones, VT616 and VT618, gave positive reactions with fimbria-specific antisera. That the gene coding for the antigen was located on the plasmid was confirmed by demonstrating that the presence of the plasmid was linked to antigen production. Western immunoblot analyses of sodium dodecyl sulfate-polyacrylamide gel electrophoresis gels showed that both clones produced a fimbrial peptide of Mr 30,000. The two recombinant plasmids were shown by Southern analysis and restriction mapping to contain the same 6-kilobase EcoRI fragment inserted in opposite orientations. Southern hybridization confirmed that this fragment is present in S. sanguis genomic DNA. The Mr 30,000 protein gene was expressed in both orientations, suggesting that the fimbrial promoter is located on the 6-kilobase fragment. These results show that at least one streptococcal fimbrial gene can be cloned and expressed in E. coli.     

Effect of immunization on susceptibility to experimental Streptococcus mutans and Streptococcus sanguis endocarditis.

It has been asserted that humoral immunity is an important potentiating factor in pathogenesis of infective endocarditis, in that prior immunization to certain bacteria may predispose the host to endocarditis caused by those organisms. If so, possible future vaccination of humans with streptococcal antigens for the prevention of dental caries might increase the susceptibility of the population to streptococcal endocarditis. To examine this hypothesis further, we immunized rabbits with killed Streptococcus sanguis or Streptococcus mutans. After complement-fixing antibody had developed, the rabbits were tested for susceptibility to experimental infective endocarditis. Rabbits with high titers of complement-fixing antibody to the infecting organism developed streptococcal endocarditis less often (13%) than animals with lower titers (69%; P less than 0.0002). These findings do not support the hypothesis that pre-immunization predisposes to infective endocarditis and lend no credence to the concept that vaccination of human subjects against dental caries might increase their susceptibility to streptococcal endocarditis. On the contrary, the results of these experiments indicate that specific antibody can confer relative immunity to infective endocarditis.     

Adherence of Streptococcus mutans and Streptococcus sanguis to salivary components bound to glass.

Adherence of radiolabeled Streptococcus mutans and Streptococcus sanguis to saliva-treated glass surfaces was studied under conditions which minimized bacteria-glass interactions. Treatment of glass with an alkylsilane solution decreased nonspecific bacterial adherence and enhanced adsorption of radiolabeled salivary components to these surfaces. Addition of Triton X-100 to the bacterial suspensions also reduced nonspecific adherence to siliconized glass, but did not affect adherence to salivary components attached to siliconized glass. Calcium stimulated S. mutans adherence to saliva-free glass, but inhibited adherence to saliva-treated glass. S. sanguis adherence to either saliva-free or saliva-treated glass was inhibited slightly at high calcium ion concentrations. Adherence of streptococci to saliva-treated glass exhibited saturation kinetics, and the numbers of binding sites on the experimental salivary pellicle and the affinity constants for bacteria-saliva attachment were determined. Preincubation of the streptococci with whole saliva decreased their capacity to adhere to saliva-treated glass, but not to saliva-free glass. Bacteria adherent to saliva-treated glass surfaces were readily desorbed by washing with saliva. The addition of homologous antisera, ammonium sulfate-precipitated immunoglobulins, or Fab fragments to the bacterial suspensions inhibited cell adherence to saliva-treated glass.     

Streptococcus sanguis surface antigens and their interactions with saliva.

Saliva-binding molecules of Streptococcus sanguis and their receptors were investigated. Streptococcal cell surfaces were extracted with a barbital buffer and examined immunochemically. Strains G9B and Blackburn, which adhere specifically to saliva-coated hydroxyapatite via immunologically related adhesins, possess 80-, 62-, and 52-kilodalton (kDa), and 52-, 42-, and 29-kDa polypeptides, respectively, which correlate with adhesion to saliva-coated hydroxyapatite. Nonadherent strains Adh- and M-5 lack these antigens. In an immunoblot overlay, the putative adhesins bound to a 73-kDa receptor present in submandibular saliva but not in parotid saliva. G9B also contains a 160-kDa surface protein which bound to an unidentified receptor in both submandibular and parotid saliva samples. Blackburn barbital-extracted components bound to 78- and 70-kDa receptors in parotid saliva. These bacterial-salivary interactions may be important in the regulation of oral ecology.