Actinobacillus actinomycetemcomitans fimbriae.

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.