Protein-based biofilm matrices in Staphylococci

Staphylococcus aureus and Staphylococcus epidermidis are themost important etiological agents of biofilm associated-infections on indwelling medical devices. Biofilm infections
may also develop independently of indwelling devices, e.g., in native valve endocarditis,
bone tissue, and open wounds. After attachment to tissue or indwelling medical devices
that have been conditioned with host plasma proteins, staphylococcal biofilms grow, and
produce a specific environment which provides the conditions for cell–cell interaction and
formation of multicellular communities. Bacteria living in biofilms express a variety of
macromolecules, including exopolysaccharides, proteins, extracellular eDNA, and other
polymers. The S. aureus surface protein C and G (SasC and SasG), clumping factor B
(ClfB), serine aspartate repeat protein (SdrC), the biofilm-associated protein (Bap), and
the fibronectin/fibrinogen-binding proteins (FnBPA and FnBPB) are individually implicated
in biofilm matrix formation. In S. epidermidis, a protein named accumulation-associated
protein (Aap) contributes to both the primary attachment phase and the establishment
of intercellular connections by forming fibrils on the cell surface. In S. epidermidis,
proteinaceous biofilm formation can also be mediated by the extracellular matrix binding
protein (Embp) and S. epidermidis surface protein C (SesC). Additionally, multifunctional
proteins such as extracellular adherence protein (Eap) and extracellular matrix protein
binding protein (Emp) of S. aureus and the iron-regulated surface determinant protein
C (IsdC) of S. lugdunensis can promote biofilm formation in iron-depleted conditions.
This multitude of proteins intervene at different stages of biofilm formation with certain
proteins contributing to biofilm accumulation and others mediating primary attachment
to surfaces. This review examines the contribution of proteins to biofilm formation in
Staphylococci. The potential to develop vaccines to prevent protein-dependent biofilm
formation during staphylococcal infection is discussed.