Coaggregation studies of the Eubacterium species.

Eubacterium species are gram-positive anaerobic rods that are frequently isolated from subgingival plaque of periodontal pockets. Five Eubacterium species were tested for their ability to coaggregate with 33 oral bacterial strains. Using visual and turbidimetric assays, coaggregation was observed among Eubacterium brachy, Eubacterium nodatum, Eubacterium alactolyticum and Eubacterium limosum strains only when tested with Fusobacterium nucleatum strains; Eubacterium saburreum displayed only weak coaggregation ability. Coaggregation between F. nucleatum and the Eubacterium species was observed over a wide range of concentrations of each organism. The F. nucleatum strains contained a heat labile and the Eubacterium species a heat stabile coaggregation receptor. Arginine, histidine, lysine and glycine inhibited the coaggregation between F. nucleatum and the Eubacterium species. Sugars and other amino acids tested did not inhibit the observed coaggregation. Rabbit anti-F. nucleatum serum completely inhibited coaggregation, but anti-E. brachy serum and normal rabbit serum did not. As these anaerobic microorganisms are frequently isolated from the same oral lesions, the surface interactions observed may be important in the pathogenesis of these polymicrobic infections.