Nearly two-thirds of all hospital-related infections are associated with biofilms, and Staphylococcus epidermidis
biofilms are responsible for 40% of infections in hip and knee replacements. The first step in biofilm formation is
bacterial attachment to a surface. This process is mediated by components on the cell wall and the implant
surface. Understanding the mechanism of bacterial surface attachment and methods to prevent it could lead to
novel and innovative approaches for preventing biofilms. The extracellular autolysin protein (AtlE) strongly binds
with polystyrene and serum-coated surfaces, and inhibiting this binding reduces surface attachment and biofilm
formation. Moreover, the R2ab subdomain of AtlE, binds not only polystyrene but also staphylococcal cell wall
components. While polystyrene is a valuable model for studying surface attachment, it is brittle and unsuitable
for biomedical implants. This project will extend prior investigations to a more clinically relevant surface, poly-
methylmethacrylate (PMMA), a material used in orthopedic and dental implants (bone cement). Prior work has
shown that nanoparticles are a valuable model for studying many aspects of protein-surface interaction. Their
colloidal stability and high surface-to-volume ratio enable studies of protein behavior when nanoparticles are
present. By examining protein binding to PMMA nanoparticles, the structural and biophysical determinants that
influence bacterial attachment during biofilm formation will be identified. Strong preliminary data demonstrate
that structural rules for these protein-surface interactions can be determined and manipulated to reduce bacterial
attachment and subsequent biofilm formation. In Aim 1, these “rules of PMMA surface attachment” will be
established using biophysical experiments. The structure and orientation of extracellular S. epidermidis proteins
on PMMA surfaces and serum-coated PMMA surfaces will be determined. In Aim 2, a novel biomaterial surface
functionalization strategy will be developed that reduces protein binding and could dramatically slow biofilm
formation on PMMA surfaces. This strategy will be developed using PMMA nanoparticles and tested on
commercially available bone cement in an in vitro biofilm reactor. Finally, in Aim 3, the R2ab domain will be used
to localize photothermally active nanoparticles to biofilms in an in vivo animal model, testing whether targeted
near-infrared photothermal therapy is a viable treatment for biofilms. Two models will be tested, including a
wound model and an osteomyelitis (bone infection) model. The goal of this basic and preclinical research is to
understand how S. epidermidis surface proteins lead to biofilms on medically relevant surfaces. The mechanistic
details of biofilm formation on PMMA surfaces will improve the understanding of how biofilms form; the new
surface treatments will establish a practical approach for slowing down biofilm development; and the targeted
nanoparticles will lead to more practical strategies for treating established biofilms. Each aspect of this project
addresses a significant challenge in the biofilm field with an innovative and biophysically motivated approach.
Ultimately, this research will lead to a more favorable outcome for patients facing a biofilm infection.
