Probing intermolecular forces that direct the formation
of Staphylococcus aureus biofilms on medical devices
Steven Lower, OSU,
Department of Geological Sciences
The rate of cardiac device implantations (e.g., prosthetic heart valves, permanent pacemakers, left ventricular assist devices, and implantable cardioverter defibrillators) has increased dramatically over the last decade because these prosthetic devices have been shown to improve survival and reduce symptoms in humans. Furthermore, the growing number of evidenced-based indications for cardiac devices, coupled with an aging US population, assures a continued increase in the implantation of cardiac devices. While cardiac implants have prolonged the lives of countless patients, they also paradoxically place these same patients at substantial risk for infection. Cardiac device infections are most commonly caused by staphylococci and carry substantial morbidity and mortality. The initial adhesion of bacteria to the device leads to the formation of a biofilm, which causes enormous clinical difficulties because bacterial biofilms are often resistant to antibiotics. Therefore, standard therapy for cardiac device infection involves surgical removal of the infected device.
At the most fundamental level, bacterial adhesion and biofilm formation are controlled by intermolecular forces between a Staphylococcus aureus bacterium and a material surface. However, it has been very difficult to probe these forces because of their seemingly infinitesimal magnitude and distance over which they operate. This seminar will describe a collaborative research project between Ohio State University and Duke University Medical Center. The broad long-term objective of this collaboration is to establish a new perspective on biofilm formation by directly quantifying the attractive or repulsive forces between a living S. aureus cell and another surface with nano- to pico-Newton resolution. This seminar will highlight some recent experiments that have used atomic force microscopy to measure forces between S. aureus and various materials including glass, polystyrene, and fibronectin in aqueous solution. These force measurements will be interpreted with some classical theories designed to model electrostatic and steric forces, and the data will be discussed in the context of the clinical outcome of patients with prosthetic devices.