Inhibition of Porphyromonas gingivalis adhesion to Streptococcus gordonii by human submandibular-sublingual saliva

Porphyromonas gingivalis W50 adheres in vitro to biofilms of Streptococcus gordonii G9B. This phenomenon is believed to facilitate the initial colonization of the oral cavity by P. gingivalis and to contribute to the maturation of dental plaque. In this report, we describe the modulating effects of human submandibular-sublingual saliva (HSMSL) on this in vitro model of intergeneric bacterial adhesion (coaggregation). HSMSL inhibited P. gingivalis adhesion to S. gordonii by 50% at a concentration of 57 μg of protein per ml. Maximum inhibitory activity was associated with a 43-kDa protein obtained by sequential Sephadex G200 gel filtration and CM52 ion- exchange chromatography of HSMSL. Pools of other column fractions of HSMSL showed no effect or were slightly stimulatory for bacterial adhesion. The binding of radioiodinated column fractions containing the 43-kDa protein by P. gingivalis was accompanied by their rapid enzymatic degradation. Treating P. gingivalis at 60°C for 30 min or with protease inhibitors (phenylmethylsulfonyl fluoride and sodium iodoacetate) reduced adherence to streptococcal biofilms. These treatments did not prevent P. gingivalis from binding soluble HSMSL saliva components, although subsequent proteolysis was nearly eliminated. These observations indicate that surface-associated proteases of P. gingivalis, either independently or in concert with adjacent surface adhesins, interact with surfaces of oral streptococci to facilitate interbacterial adhesion. The adhesion-blocking properties of HSMSL, particularly the 43-kDa protein, may represent an important host defense mechanism in the oral cavity.