Aggregation substance-mediated adherence of Enterococcus faecalis to immobilized extracellular matrix proteins

Aggregation substance (AS) of Enterococcus faecalis (E. faecalis), a sex ph eromone plasmid encoded cell surface protein, mediates the formation of bac terial aggregates, thereby promoting plasmid transfer. The influence of pAD 1-encoded AS, Asa1, on binding to immobilized extracellular matrix proteins was studied. The presence of AS increased enterococcal adherence to fibron ectin more than eight-fold, to thrombospondin more than four-fold, to vitro nectin more than three-fold, and to collagen type I more than two-fold (P < 0.001). In contrast, binding to laminin and collagen type IV occurred inde pendently of AS. Adherence of the constitutively AS expressing E. faecalis OG1X(pAM721) to immobilized fibronectin was found to be approximately five times higher than that of Staphylococcus aureus Cowan and approximately 30 times higher than that of Streptococcus bovis. Investigation of strains wit h various deletions within the structural gene of asa1 suggests that attach ment to immobilized fibronectin is mainly mediated by amino acids within th e variable region or by neighbouring residues. Thus, AS may promote adheren ce to injured epithelium and endothelium, where extracellular matrix protei ns are exposed, thereby facilitating colonization and infection. (C) 2001 A cademic Press.