The Structure, Orientation, and Competitive Interactions of S. Epidermidis Biofilm Proteins on Surfaces

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.