Identification of 40-kDa outer membrane protein as an aggregation factor of Porphyromonas gingivalis to Streptococcus gordonii.

Porphyromonas gingivalis, an important pathogen in periodontitis, aggregates with other oral microorganisms such as Streptococcus gordonii. We previously succeeded in gene cloning the 40-kDa outer membrane protein (OMP) from P. gingivalis. Although recombinant (r) 40-kDa OMP itself did not show aggregation activity, the affinity-purified antibody against 40-kDa rOMP inhibited the aggregation activity of P. gingivalis cells toward S. gordonii which is one of the first oral bacteria to colonize on tooth surfaces and can be expected to support subsequent colonization of other bacteria. In this study, in order to clarify the pathological role of 40-kDa OMP, we used a cross-linking reagent to construct a polymeric form of r40-kDa OMP and examined its aggregation activity. The polymeric r40-kDa OMP significantly expressed aggregation activity with S. gordonii cells. Moreover, the antibody against r40-kDa OMP inhibited the aggregation activity of the polymeric r40-kDa OMP. These findings clearly demonstrate that 40-kDa OMP, as a multivalent form, is one of the important aggregation factors on the cell surface of P. gingivalis.