In the early stages of infection, bacteria attach to host tissue. Interactions between host and bacterial proteins are also likely to play an important role in the maintenance and dissemination of infection. Bacteria such as Staphylococcus aureus can also form difficult to eradicate aggregates, known as biofilms, on the surfaces of in-dwelling medical devices. We are studying bacterial proteins involved in host-pathogen interactions and biofilm formation. Using techniques such as nuclear magnetic resonance spectroscopy, X-ray crystallography, isothermal titration calorimetry, surface plasmon resonance and multi-angle light scattering we have shown that some of these proteins have unsual structures and mechanical properties that are likely to play an important role in their function.