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Fibronectin binding to protein A-containing staphylococci

Fibronectin (Fn) was found to bind to protein A-containing isolates of Staphylococcus aureus, but not to mutant strains devoid of this protein nor to clinical isolates of S. epidermidis. Fn was purified from human plasma by affinity chromatography on gelatin-Sepharose. After elution with 4 M urea, sodium dodecyl sulfate-polyacrylamide gel electrophoresis of purified material detected no immunoglobulin contamination. This purified Fn was radiolabeled with 125I and used in binding assays. Quantitatively, Fn binding was directly correlated with the cellular protein A content of the various strains tested. Mannitol salt broth preculture or organisms resulted in a reduction of their cellular protein A and a decrease in Fn binding by these cells. However, soluble protein A maximally inhibited the binding of radiolabeled Fn to protein A-positive strains of staphylococci by only 50%, indicating the possibility of multiple Fn binding sites. Fn's binding to protein A-containing S. aureus strains may play a role in the pathogenicity of these organisms by promoting their attachment to and subsequent invasion of host tissues.