Streptococcus anginosus adheres to vascular endothelium basement membrane and purified extracellular matrix proteins

The mechanisms of bacterial adherence in the initial stages of native valve endocarditis are unclear, especially in patients without valve disease or the presence of a platelet-fibrin thrombus. Extracellular matrix may act as a ligand in areas of exposed basement membrane on the endothelial monolayer. In this study, adherence of 55 clinical blood and 21 oral viridans streptococcal isolates was examined using purified extracellular matrix compounds. The majority of blood and oral isolates exhibited adherence to purified laminin, fibronectin, and fibrinogen, with lesser adherence to type I and IV collagens. Adherence to laminin and fibronectin was concentration dependent, saturable, and competitively inhibited with soluble ligand. A Streptococcus anginosus isolate and other viridans strains exhibiting a strong laminin adherence phenotype bound extensively to the endothelial aspect of human and porcine valve tissue sections and were inhibited by soluble laminin and anti-laminin antibody fragments. Using a novel native porcine valve explant adherence model, we localized binding to areas of exposed basement membrane by confocal and scanning electron microscopy. These studies support the hypothesis that bacterial adherence to exposed basement membrane plays a role in the initial phase of native valve endocarditis.