Bacterial Adhesion and Interaction with Biomaterial Surfaces - Biointerfaces: Where Material Meets Biology - page 366

The diculty in treatment of device-centered infections is primarily re-
lated to biofilm formation. Bacteria adhere, colonize on the surface, and
produce a polysaccharide slime forming a biofilm, which can protect bac-
teria from host microbicidal systems and antimicrobial agents. 8-10 In add-
ition, antibiotic resistant strains including Staphylococcus aureus and
Staphylococcus epidermidis have proven dicult to be treated by standard
antibiotic therapy after colonization on the prosthetic surface. 11,12 In the
case of blood-contacting devices, a biofilmmay continuously release bacteria
into the blood stream and interact with platelets resulting in platelet acti-
vation 13 and thrombus formation. 14 Despite intense research efforts in
the last decades, the problems associated with biofilms as well as the in-
creasing levels of antibiotic resistance pose severe challenges in health care-
associated infections.
A broad range of biomaterials, both natural and synthetic, encompassing
metals, ceramics, synthetic polymers, biopolymers, self-assembled systems,
nanoparticles, carbon nanotubes and quantum dots, are widely applied in
medical devices. 15 The application of newly developed biomaterials must
satisfy certain performance criteria such as biocompatibility and long-term
stability. When a biomaterial is implanted into the body, biomaterials in-
duce different biological responses. 16,17 Generally, proteins are adsorbed
onto the biomaterial surfaces immediately upon implantation in a range of
conformations from native to denatured, and mediate the subsequent bio-
logical reactions. A number of different cells such as monocytes, leukocytes,
platelets, and bacteria arriving at the biomaterial surfaces will interact with
the adsorbed protein layer as well as materials. Thus the initial protein ad-
sorption onto a biomaterial surface plays a key role in how the body re-
sponds to an implanted biomaterial. 18 Understanding the host responses of
implants to bacterial adhesion is important for improving the biocompati-
bility of biomaterials.
The most common bacteria leading to nosocomial infection include
Staphylococcus, Enterococci, Pseudomonas and Candida species. 7,19 Particu-
larly, staphylococci are the most commonly diagnosed microorganisms in
microbial infection on blood-contacting devices. 7 S. aureus and S. epi-
dermidis are two major opportunistic pathogens of this genus. S. aureus,a
coagulase-positive staphylococci, is much more virulent and aggressive,
and synthesizes an array of toxins and other virulence factors, causing a
range of acute and pyogenic infections. S. aureus has received significant
attention and been intensively studied. 20-23 S. epidermidis, a coagulase-
negative staphylococci, ranks first among the causative agents of nosoco-
mial infections and represents the most common source of infections on
indwelling medical devices such as prosthetic heart valves and joint
prostheses. 24,25 The main defined virulence factor associated with S. epi-
dermidis is its ability to colonize on biomaterials and form biofilms which
are recalcitrant to the deleterious action of antibiotics and impedes the
host immune response. 26

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