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Characterization of the fibrinogen and fibrin adhesin of Staphylococcus aureus Martin, Alexis Wilma


The interaction between Staphylococcus aureus and cross-linked and non-cross-linked fibrin has been characterized and the cell wall component mediating fibrinogen induced clumping has been identified. Binding of S. aureus to fibrin and clumping of the cells in fibrinogen, appear to be mediated by the same cell wall component, called clumping factor (Clf). The binding of S. aureus to fibrin was maximal at 37°C with a pH optima of 6-8 and was independent of divalent cations. The interaction between the two surfaces occurred within minutes and once bound, cells were difficult to remove. The fibrin-binding reaction was inhibited by 1M NaCl and 4M urea but not by any protein, glycoprotein, glycolipid, or any specific sugar tested. Heating the cells, treating them with protease, or acetylating amino groups abrogated their binding activities. A glycoprotein, believed to be the Clf, has been partially purified from lysostaphin solubilized cell walls of S. aureus, Clf+ strains, by affinity chromatography on immobilized fibrinogen. The Clf active fraction bound to fibrinogen and eluted with 2M NaCl. Analysis of the fraction by gel electrophoresis revealed a single band, molecular weight approximately 90,000 daltons, which stained positively for protein and carbohydrate. This glycoprotein could not be identified in cell walls of a Clf negative strain of S. aureus. Immunoelectrophoretic analysis of the clumping factor fraction, showed that it formed a single precipitin line with anti- Clf+ S. aureus antiserum (anti-S. aureus-1) but not with antiserum raised against the Clf- mutant. An assay was developed to quantitate the soluble Clf, and showed that the Clf absorbed or neutralized specific clumping inhibiting antibodies present in anti-S. aureus-1, that prevented fibrinogen induced clumping of S. aureus. Other Clf- mutants of S. aureus and non-staphylococcal bacteria were examined for fibrin and fibrinogen binding and fibrinogen clumping activites. The majority of bacteria observed that could bind to fibrin and fibrinogen, could not clump in the presence of fibrinogen.' A model is presented to describe adhesins that bind to fibrinogen but are unable to form cell-aggregates.

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