Binding of oral streptococci to human fibrinogen

The interaction of oral streptococci with human fibrinogen was investigated . Streptococcus gordonii was chosen as a representative species to study th e binding to fibrinogen. S. gordonii DL1 adhered to immobilized fibrinogen and bovine serum albumin. Binding to immobilized fibrinogen was saturable, concentration and temperature dependent. The binding of S. gordonii DL1 to fibrinogen was inhibited by anti-fibrinogen antibody. Heating of the bacter ia for 1 h at 95 degreesC resulted in 90% inhibition of the binding. Trypsi n treatment of the bacteria resulted in decreased binding. Neither lipoteic hoic acid nor culturing of the bacteria in a sucrose-supplemented medium ha d any effect on the binding. S. gordonii, Streptococcus sanguinis, Streptoc occus mitis, and Streptococcus oralis bound to the immobilized fibrinogen, but mutans streptococci did not. None of the oral streptococci tested bound to the fibrinogen in fluid phase. These results suggest that the binding o f S. gordonii DL1 to immobilized fibrinogen is mediated through a specific protein adhesin-receptor interaction, and fibrinogen acts as a cryptitope.