No abstract

Freshly isolated Actinobacillus actinomycetemcomitans strains were found to possess fimbriae. These appendages appeared to be irreversibly lost after 30 to 40 subcultures in the laboratory. The fimbriated strains were associated with a specific type of colonial morphology designated SP (Star Positive); the non‐fimbriated variant colony was designated SN (Star Negative). The fimbriae were approximately 5 nm wide and could be several μm in length. The fimbriated cells tended to aggregate readily whereas the non‐fimbriated cells formed uniform suspensions. Three stains of fimbriated A. actinomycetemcomitans isolated from different patients were compared to their non‐fimbriated variants for attachment to hydroxyapatite (HA) and saliva coated hydroxyapatite (SHA). Two of the fimbriated variants exhibited a 3‐ to 4‐fold enhancement of attachment to HA and SHA over their non‐fimbriated variant. However, there did not appear to be any specificity for SHA over HA. One strain (Pag) showed no major differences in attachment of the fimbriated or non‐fimbriated variant, albeit the fimbriae were indistinguishable from those of the other A. actinomycetemcomitans strains. Thus, there may be molecular differences among fimbriae of various A. actinomycetemcomitans strains which determine both their tissue specificity and their affinity for particular substrates.

Adherence of Porphyromonas gingivalis to early plaque bacteria, such as Streptococcus gordonii, is considered an important colonization mechanism. The molecules that mediate this interspecies binding have not been determined. Fimbriae were prepared from P. gingivalis 33277 by mild agitation, ammonium sulfate precipitation and DEAE-Sepharose chromatography. In a nitrocellulose blot adherence assay, purified fimbriae inhibited S. gordonii G9B-P. gingivalis 33277 binding by up to 54%. In addition, fimbriae bound to S. gordonii cells in a dot-blot assay. Incubation of fimbriae with S. gordonii cells followed by washing, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), electroblotting and probing with P. gingivalis antibodies also revealed that the fimbriae bind to S. gordonii. In contrast, S. gordonii did not interact with fimbriae that were first subjected to SDS-PAGE and electroblotting or deposited on a nitrocellulose membrane, suggesting that conformational determinants of the fimbriae may be important in binding. The results indicate that binding between P. gingivalis and S. gordonii is mediated, at least in part, by the porphyromonads' fimbriae.

Adherence of Porphyromonas gingivalis to strains of Streptococcus sanguis and Streptococcus mitis deposited on nitrocellulose paper was investigated. A variety of laboratory strains and clinical isolates of P. gingivalis bound to both S. sanguis and S. mitis. Binding of P. gingivalis to all but one of the streptococci was not inhibited by salivary molecules. Pretreatment of P. gingivalis with periodate and pretreatment of S. sanguis and S. mitis with pronase decreased binding, suggesting that adherence may be mediated by a protein on the streptococci interacting with a carbohydrate on P. gingivalis. Binding was not inhibited by a selection of simple sugars. The ability to adhere to early plaque bacteria such as S. sanguis and S. mitis may be important in the colonization of the mouth by P. gingivalis.

A mixture of saliva-coated hydroxyapatite beads and radioactively labeled bacteria has been employed as an in vitro model for the initial phase of dental plaque formation. Adsorption in this model can be expressed by the Langmuir adsorption isotherm, and the adherence of oral streptococci can be expressed as the product of the affinity constant (K.) and the number of binding sites (N), KaN. With this approach, Streptococcus sanguis serotype 1 strains adhered better (KaN = [187 ± 72] X 10-2) than serotype 2 strains (KaN = [97 + 84] X 10-2); a t