Quantification of S. aureus adhesion to fibronectin using optical tweezers

Biomaterial infection, a common cause of medical device failure, is initiated by bacterial adhesion to an adsorbed protein layer on the implant surface. This adhesion is thought to be mediated by specific molecules present on the bacterial cell surface. We have used optical tweezers to measure the adhesive force between a single bacterium and a protein-coated surface. A bacterium was optically trapped and brought in contact with a 10-μm diameter polystyrene microsphere coated with fibronectin. The minimum force required to detach the cell from the bead was determined over a range of fibronectin concentrations. The detachment forces were integer multiples of a 25-pN base value that was independent of coating concentration; we propose that the variation in force is related to the number of bonds formed.