Microfluidic parallel plate flow chambers provide a method for evaluating the role of molecular mechanics in the dynamic adhesion of cells or bacteria. We use optical microscopy for real-time monitoring of adherent cells in laminar flow conditions to study a counter-intuitive observation. Escherichia coli, our most common intestinal bacteria, require shear stress to bind to surfaces coated with mannose, a carbohydrate expressed on many host cells. In fact, even cells that are already bound will detach if the flow is turned down. Because these flow chambers involve bacteria binding to surfaces similar to biomaterial or tissue surfaces in our body, these experiments shed light on bacterial adhesion in vivo. However, flow chamber experiments can be carefully controlled so that they can also be used to determine the mechanism behind this unusual behavior. We show that the effect of shear stress on transport of bacteria to the surface cannot explain these results. Rather, increased shear stress causes bacteria to roll instead of detach and to switch to a stationary mode of adhesion.

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