EFFECT OF BINDING OF FIBRINOGEN TO EACH BACTERIUM ON COAGGREGATION BETWEEN PORPHYROMONAS-GINGIVALIS AND STREPTOCOCCUS-ORALIS

Fibrinogen inhibits the coaggregation between Porphyromonas gingivalis and Streptococcus oralis. In this study, we determined which bacteriu m interacts with fibrinogen in this inhibitory process. Although prein cubation of each bacterium with fibrinogen did not inhibit coaggregati on, its activity was completely eliminated by the addition of protease inhibitors such as N-ethylmaleimide (NEM), p-chloromercuriphenyl sulf onate and N alpha-p-tosyl-L-lysine chloromethyl ketone to the preincub ation mixture with fibrinogen and P. gingivalis. However, the inhibiti on of coaggregation was not found after preincubation of S. oralis wit h fibrinogen in the presence or absence of the protease inhibitors. La belled materials were recovered from the extract of P. gingivalis cell s incubated with radioiodinated fibrinogen in the presence of NEM but not in the absence of NEM. In the binding experiment, P. gingivalis sh owed a much higher binding activity to fibrinogen than S, oralis. Thes e findings suggest that fibrinogen and its fragment(s) may mask direct ly or indirectly the aggregation site with S. oralis on the P. gingiva lis cells in its inhibitory process of coaggregation.