Bacterial Adhesion and Interaction with Biomaterial Surfaces - Biointerfaces: Where Material Meets Biology - page 373

promote the adherence of bacteria. For example, Tegoulia and Cooper
found pre-adsorption of Fg on SAMs coated surface minimized the effect
of the surface properties of the substrate and adherence of S. aureus
was increased on all SAMs surfaces. 35 The increase in adhesion of S. aureus
by Fg is due to the receptor-ligand interactions between protein and Fg-
binding MSCRAMM clumping factors on cell surface. 32,33 A Fg-binding
adhesin gene was found on S. epidermidis cell surfaces from central venous
catheters-associated and orthopedic implant-associated infections, demon-
strating that Fg also increased the adhesion of S. epidermidis to biomaterial
surfaces. 114
Fn is another main plasma protein responsible for forming a condition
film on implanted biomaterials. It can bind a variety of extracellular mol-
ecules including fibrin, heparin, and collagen, and plays a key role in cell
adhesion and proliferation. 115,116 However, the effect of Fn on adherence of
bacteria is highly variable. On the one hand, numerous studies have found
that Fn facilitates bacterial adhesion to biomaterials including S. aureus and
S. epidermidis. 38,117-119 Similar to the mechanism of enhancement of bac-
terial adhesion by Fg, Fn-binding proteins were found on S. aureus 120 and
S. epidermidis 46 cell surfaces, respectively, and contributed to initial bacterial
adhesion. On the other hand, several studies showed that Fn had no effect or
even inhibited the adhesion of S. epidermidis to protein-coated sur-
faces. 121-123 Inhibition of adhesion is likely due to the production of an
exopolysaccharide by S. epidermidis that influences interactions with
protein-coated surfaces 121 or the adhesion of S. epidermidis to Fn-coated
surface is not a specific adhesion. 123 The conflicting results indicate the
most basic mechanisms of binding between S. epidermidis and Fn-coated
surface are unknown yet, and more work should be done to examine the role
of Fn in adhesion of bacteria to surfaces, especially in light of interactions of
protein-cell at molecular level on substrata with different physicochemical
properties.
Conformational structure and orientation of plasma proteins may influ-
ence bacterial adhesion. Fn is a dimer of two similar polypeptides linked by
disulfide bonds at the carboxyl terminus, and possesses several functional
domains that binds to a variety of extracellular molecules such as heparin
and collagen. 124 There are two physiologically relevant binding sites to ad-
here to bacterial cell surface, which are located at the N-terminus and the
C-terminus of Fn. S. epidermidis was shown to exhibit a different adhesion
response when Fn was oriented with the C-terminus versus the N-terminus
bound to the surface. 125 Holmes et al. studied the bacterial interactions with
intact or fragments of Fn by surface plasmon resonance technique and
found S. aureus preferentially binds to the Fn N-terminal region whereas
S. epidermidis binds to the C-terminal domain. 126 Vadillo-Rodriguez et al.
found that Fn molecules adopt a more extended conformation on hydro-
phobic than hydrophilic Ti6A14V surfaces and the extended conformation of
the proteins facilitates the exposure of specific sites for adhesion, resulting
in higher bacterial attachment. 127 We used immuno-AFM (atomic force

d n 3 r 4 n g | 3

.