Coaggregation between Porphyromonas gingivalis and Treponema denticola

To elucidate an ecological profile of several periodontopathogens, the authors examined the coaggregation between cells of Porphyromonas gingivalis and oral bacterial strains including Treponema denticola in vitro. Coaggregation between cells of plaque bacteria was examined by visual assay and phase-contrast microscope. P. gingivalis cells coaggregated with strains of T. denticola and Treponema socranskii subspecies socranskii, but did not coaggregate with T. socranskii subspecies buccale, T. socranskii subspecies paredis, Treponema vincentii, or Treponema pectinovorum. The extracted hemagglutinin from P. gingivalis was active agglutinating T. denticola cells. Addition of serum and saliva somewhat affected the coaggregation, but no effects of tested sugars or amino acids were found. Heat treatment of T. denticola cells did not reduce the coagregation: heat treatment of P. gingivalis cells eliminated it. Growth inhibitory activity among these bacterial species was examined by the stab culture method. Strains of T. denticola ATCC 35404 and 35405 and T. vincentii inhibited the growth of some P. gingivalis strains, but not others. No strain of Treponema was inhibited by black-pigmented anaerobic rods. The coaggregation observed between P. gingivalis and T. denticola indicates the potential importance of their simultaneous existence in human periodontal pockets and development of the disease.