To block unspecific interactions with IgG-binding proteins, the membrane was incubated for 1 h with 5% (vol/vol) goat serum (Sigma) dissolved in TBS buffer containing 0.3% (wt/vol) bovine serum albumin (BSA; Sigma) as previously described (26). Spa in S. aureus MR23 biofilm matrix and cell wall fractions was detected using rabbit IgG(Sigma) and goat anti-rabbit IgG-HRP (Bio-Rad). The primary
antibody and secondary antibody were diluted 20,000-fold in TBS-T. Samples were separated and transferred as mentioned above. The membranes were incubated for 1 h with 3%BSA (Sigma) in TBS-T. Themembrane was treated with the primary antibody at 25°C for 1 h and then washed twice with TBS-T. Subsequently, themembrane was incubated in TBS-T containing the secondary antibody. After washing three times with TBS-T, the immunoreactive signals were detected with an ECL-plus detection kit (GE Healthcare).