Adherence of Staphylococcus aureus fibronectin binding protein A mutants: an investigation using optical tweezers

Bacterial adhesion to extracellular matrix proteins plays a major role in infections of host tissue and medical devices. In some species of gram-positive cocci, this adhesion is mediated by specific molecules present on the bacterial cell surface. We have used optical tweezers to dynamically measure the adhesive force between an individual Staphylococcus aureus bacterium and a fibronectin-coated surface. A bacterium was optically trapped and brought in contact with a 10-microm diameter polystyrene microsphere coated with fibronectin. The force required to detach the cell from the microsphere was measured by tracking the displacement signals of the trapped cell on a quadrant photodiode throughout the detachment process for a series of S. aureus strains expressing fibronectin-binding proteins with various degrees of mutation. The single-bond rupture forces ranged between 15 and 26 pN depending on the extent of mutation. No binding was observed in the strain with the highest degree of mutation. These results confirm that multiple regions of the S. aureus fibronectin adhesin participate in the binding process and provide further insight into the role of these regions in the adhesive process.