title: Inhibition of fibrinogen reaction by polysaccharide of encapsulated Staphylococcus aureus.
abstract: Encapsulated and nonencapsulated strains of Staphylococcus aureus which lack coagulase or clumping factor (bound coagulase), or both, were examined for the antigen associated with the fibrinogen-cell clumping reaction. Extracts of the cells were tested for the ability to react with fibrinogen or to inhibit fibrinogen precipitation. Antisera prepared against encapsulated (coagulase-positive, clumping factor-negative) variants, as well as against nonencapsulated wild-type (coagulase-positive, clumping factor-positive) S. aureus strains, contained high titers of clumping-inhibiting antibody. When coagulase-negative, clumping factor-negative mutants were the immunizing agents, antisera contained no demonstrable clumping-inhibiting antibody. Phenol extracts of all coagulase-positive strains tested precipitated fibrinogen, regardless of the ability of cells to clump in the presence of fibrinogen. Polysaccharide extracts of encapsulated, clumping factor-negative strains inhibited this fibrinogen-precipitating activity, whereas similar extracts of nonencapsulated staphylococci did not inhibit the fibrinogen reaction. From these results, it appeared that the coagulase-positive, encapsulated staphylococci which do not clump in fibrinogen solution possess clumping factor, but that their capsular polysaccharide inhibits clumping activity. These findings suggested a closer association of clumping factor and coagulase than is now recognized.
mesh_terms: D003030:Coagulase; D005340:Fibrinogen; D007106:Immune Sera; D005779:Immunodiffusion; D011135:Polysaccharides, Bacterial / Q000494:pharmacology*; D013210:Staphylococcus / Q000201:enzymology / Q000276:immunology; D014774:Virulence
chemical_list: D003030:Coagulase; D007106:Immune Sera; D011135:Polysaccharides, Bacterial; D005340:Fibrinogen