The role of protein A in the attachment of staphylococci to influenza-infected cells.

The adherence of staphylococcal protein A-containing Cowan I bacteria to influenza-infected cells was enhanced up to 5 times following incubation of the monolayers with antiinfluenzal serum, but not following treatment with nomimmune serum. Significantly increased binding of Cowan I bacteria was detected at antiinfluenzal serum dilutions as high as 1:40,960. None of the several antibody concentrations tested enhanced the binding of staphylococcal protein A-negative staphylococci. In addition, extracellular staphylococcal protein A was found to inhibit complement-mediated cytolysis of antibody-coated, virus-infected cells. The possible significance of staphylococcal protein A in the synergistic interaction between staphylococcal and influenza virus infections is discussed.