Actinobacillus actinomycetemcomitans serotype b lipopolysaccharide mediates coaggregation with Fusobacterium nucleatum.

Purified Actinobacillus actinomycetemcomitans serotype b lipopolysaccharide (LPS) was found to be able to bind Fusobacterium nucleatum cells and to inhibit binding of F. nucleatum to A. actinomycetemcomitans serotype b. Sugar binding studies showed that the requirements for binding of A. actinomycetemcomitans serotype b LPS to the F. nucleatum lectin are the presence of a metal divalent ion, an axial free hydroxyl group at position 4, and free equatorial hydroxyl groups at positions 3 and 6 of D-galactose, indicating that the beta-N-acetyl-D-galactosamine in the serotype b LPS trisaccharide repeating unit is the monosaccharide residue recognized by the F. nucleatum lectin. These data strongly suggest that A. actinomycetemcomitans serotype b LPS is one of the receptors responsible for the lactose-inhibitable coaggregation of A. actinomycetemcomitans to fusobacteria.