Role played by serum, a biological cue, in the adherence of Enterococcus faecalis to extracellular matrix proteins, collagen, fibrinogen, and fibronectin

Background. Most previous studies have found that Enterococcus faecalis isolates do not show significant adherence to fibronectin and fibrinogen. Methods. The influence of various conditions on E. faecalis adherence to extracellular matrix (ECM) proteins was evaluated using a radiolabeled-cell adherence assay. Results. Among the conditions studied, growth in 40% horse serum (a biological cue with potential clinical relevance) elicited adherence of all 46 E. faecalis strains tested to fibronectin and fibrinogen but not to elastin; adherence levels were independent of strain source, and adherence was eliminated by treating cells with trypsin. As previously reported, serum also elicited adherence to collagen. Although prolonged exposure to serum during growth was needed for enhancement of adherence to fibrinogen, brief exposure (< 5 min) to serum had an immediate, although partial, enhancing effect on adherence to fibronectin and, to a lesser extent, collagen; pretreatment of bacteria with chloramphenicol did not decrease this enhanced adherence to fibronectin and collagen, indicating that protein synthesis is not required for the latter effect. Conclusion. Taken together, these data suggest that serum components may serve (1) as host environmental stimuli to induce the production of ECM protein-binding adhesin(s), as previously seen with collagen adherence, and also (2) as activators of adherence, perhaps by forming bridges between ECM proteins and adhesins.