Expression of staphylococcal protein Sbi is induced by human IgG

Protein Sbi is an IgG- and beta(2) glycoprotein I-binding protein on the su rface of Staphylococcus aureus. In most strains, the amount of protein Sbi on the cell surface is very low under normal growth conditions. However, he re we show that after growth in the presence of human serum, the amount is significantly increased. In S. aureus strain 8325-4, the observed increase is concentration-dependent and the highest level is found approximately 2 h after serum addition. The active molecule in serum was found to be IgG, wh ich causes an increase of surface-located protein Sbi in S. aureus strain 8 325-4, in the clinical isolates tested as well as in protein A-negative mut ants. Thus, the results suggest that binding of IgG to protein Sbi upregula tes protein Sbi synthesis. (C) 2000 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.