Levels of Staphylococcus aureus recovered from intra-aortic patches in passively immunized mice (A), and antibody titers (expressed as mean absorbance450 ± SEM) that remained in serum specimens from individual mice in each immunization group (B). Mice were immunized with 1 mg of isotypic control murine IgG1 (circles), 1 mg of antibody to the A domain of clumping factor A (anti-rAClfA; squares), 0.5 mg of anti-rAClfA plus 0.5 mg of antibody to the A domain of fibronectin-binding protein A (anti-rAFnBPA; triangles), or 1 mg of anti-rAClfA plus 1 mg of anti-rAFnBPA (diamonds). Horizontal black bars, mean values. CFU, colony-forming units; ND, not determined. *P < .01, compared with the isotopic control; §P < .01, compared with anti-rAClfA.