Eubacterium brachy. Reactivity in in vitro bone resorptive bioassay.

Recent studies have demonstrated an association of Eubacterium sp. with the subgingival microflora of patients with chronic periodontitis. One species, Eubacterium brachy, was evaluated to determine the possible mechanisms by which this microorganism may contribute to this disease. An extracellular antigen was identified in the culture supernatant which reacted with antibodies in human sera. This antigen was isolated by methanol precipitation and purified by gel filtration. The purified extracellular antigen was reacted in vitro with 45CaCl2-labeled fetal rat bone in a bone resorptive bioassay. This antigen was shown to have a molecular weight of 170,000, to share a line of identity with a sonicated preparation of E. brachy whole cells and to result in increased 45CaCl2 release from fetal rat bones when cultures were exposed to the purified extracellular antigen at concentrations of 10 to 53 micrograms/ml.