Coaggregation among periodontal pathogens, emphasizing Bacteroides gingivalis –Actinomyces viscosus cohesion on a saliva-coated mineral surface

Abstract

Teeth offer nonshedding surfaces on which a wide range of bacterial species accumulate as thick, cohesive plaques. Intergeneric coaggregation mediated by specific recognition between surface "cohesins" is thought to contribute to both the cohesiveness of plaque and the sequence in which bacteria colonize the tooth surface. There is some evidence that Gram-positive species, like the efficient tooth colonizer Actinomyces viscosus, enhance subsequent tooth colonization by the more virulent periodontal pathogen Bacteroides gingivalis. To study their mechanism of cohesion, we have developed an in vitro assay that measures the sequential binding of tritium-labeled B. gingivalis to A. viscosus adsorbed to saliva-coated hydroxyapatite beads, mimicking teeth (actinobeads). The assay yields equilibrium and kinetics data amenable to statistical analysis. The presence of A. viscosus significantly increased the number of B. gingivalis cells bound. Inhibition studies were conducted to test the sensitivity of binding to heat; to various saccharides and sugar amines; to proteolytic treatment of Bacteroides; and to incorporation of various chaotropic agents, increased KCl, and saliva in the suspension buffer. Heating the Bacteroides cells but not the actinobeads diminished Bacteroides adherence. Proteolysis and various saccharides had little, if any, effect. Among chaotropic agents, NaSCN and LiCl reduced numbers of cells bound by 40%, but tetramethylurea had no effect. Increasing the ionic concentration of KCl reduced binding by 50 to 60%. Diluted saliva showed a concentration-dependent inhibition of B. gingivalis adherence to actinobeads. To begin examining B. gingivalis surface molecules significant to these reactions, lipopolysaccharide was extracted by the phenol-water method and analyzed by biochemical assays and polyacrylamide gel electrophoresis.(ABSTRACT TRUNCATED AT 250 WORDS)

Adhesion of Actinomyces viscosus to Porphyromonas (Bacteroides) gingivalis-coated hexadecane droplets

“…to saliva-coated hydroxyapatite and to hydrophobic gels; however, whereas adsorption to the hydrophobic gel was inhibited by Tween 80, adhesion to saliva-coated hydroxyapatite was unaffected (3). Indeed, the common use of BSA as a blocking agent in oral adhesion studies by researchers interested in isolating the lectinlike or other complementary binding components (7,27,30) bic interactions and stereochemical binding in adhesion of oral streptococci to saliva-coated hydroxyapatite was first proposed by Doyle and coworkers in 1982 (4). However, the mechanism by which this might occur remains unclear.…”

“…In recent years, the role of interbacterial adhesion (coadhesion) in dental plaque ecology has drawn increasing interest (15). Whereas adhesion to freshly cleaned tooth surfaces occurs rapidly, the majority of microorganisms in maturing dental plaque are bound to one another rather than to the salivary pellicle on the tooth surface (5,7,15). Certain bacteria may adhere preferentially to preformed plaque rather than directly to the tooth surface (5).…”

“…Certain bacteria may adhere preferentially to preformed plaque rather than directly to the tooth surface (5). Finally, coadhesion between interdependent species in dental plaque may promote synergistic physiological relations (7,17).…”

“…Indeed, most studies to date have employed so-called coaggregation assays, in which aqueous suspensions of two strains are mixed and the degree of association is determined visually (degree of clumping) or by quantitative means (6,7,16,18). This approach, while simple to perform, is difficult to observe at the electron microscope level without altering cell-cell orientation or distance.…”

“…For example, Liljemark et al used a continuous layer of Streptococcus sanguis cells affixed to plastic and enamel surfaces with a commercial adhesive (Cell-TAK) to study coadhesion with Haemophilus parainfluenzae and Streptococcus sobrinus (17). Ellen and coworkers have studied attachment of Bacteroides gingivalis to preformed layers of Actinomyces viscosus strains on salivacoated hydroxyapatite beads (7,27). The technical complexities of preparing the substratum, coating it with the first species, and measuring coadhesion of the second species prompted us to search for a simpler solution which would also be amenable to light and electron microscopy.…”