Submitted on January 26, 2005
Accepted on May 3, 2005
Characteristics of a New Staphylococcus aureus-RBC Adhesion Mechanism Independent of Fibrinogen and Immunoglobulin G under Hydrodynamic Shear Conditions
Pyong Kyun Shin1, Parag Pawar2, Konstantinos Konstantopoulos2, and Julia M Ross1*
1 Department of Chemical and Biochemical Engineering, University of Maryland Baltimore County, Baltimore, MD, USA
2 Department of Chemical & Biomedical engineering, Johns Hopkins University, Baltimore, MD, USA
* To whom correspondence should be addressed. E-mail: jross{at}umbc.edu.
S. aureus infection begins when bacterial cells circulating in blood adhere to components of the extracellular matrix, or endothelial cells of the host and initiate colonization. S. aureus is known to exhibit extensive interactions with platelets. S. aureus is also known to bind to red blood cells (RBC) in the presence of plasma proteins such as fibrinogen and immunoglobulin G (IgG). Here we report a new binding mechanism of S. aureus to RBC independent of those plasma proteins. To characterize the new adhesion mechanism, we experimentally examine the binding kinetics and molecular constituents mediating the new adhesive interactions between S. aureus and RBCs under defined shear conditions. The results demonstrate that the receptors for fibrinogen (Clumping factor A) and IgG (protein A) of S. aureus are not involved in the adhesion. S. aureus binds to RBCs with maximal adhesion at the shear rate 100 s-1 and decreasing adhesion with increasing shear. The heteroaggregates formed after shear are stable when subjected to the shear rate 2000 s-1, indicating that intercellular contact time rather than shear forces controls the adhesion at high shear. S. aureus binding to RBC requires plasma, and 10% plasma is sufficient for maximal adhesion. Plasma proteins involved in the cell-cell adhesion such as fibrinogen, fibronectin, von Willebrand factor, immunoglobulin G, thrombospondin, laminin, and vitronectin are not involved in the observed adhesion. The extent of heteroaggregation is dramatically reduced upon RBC treatment with trypsin, chymotrypsin, or neuraminidase suggesting that the receptor(s) mediating the heteroaggregation process is a sialylated glycoprotein on RBC surface. Adhesion is divalent cation-dependent, and also blocked by heparin. This work demonstrates a new mechanism of S. aureus - RBC binding under hydrodynamic shear conditions via unknown RBC sialoglycoprotein(s). The binding requires plasma protein(s) other than fibrinogen or IgG, and does not involve the S. aureus adhesins ClfA or protein A.
