Bacteria under pressure: response to AFM nanoindentation and to spatially organized microtopographic surface patterns

The content of this talk comprises two different parts. In the first part, an atomic force microscopy (AFM)-based approach is described to probe the mechanical properties of individual bacterial cells. It is demonstrated that both gram-positive and gram-negative bacteria exhibit a viscoelastic response to an external compressive force applied by an AFM tip. In particular, cells display a viscoelastic solid-like behavior that is characterized by an instantaneous elastic deformation followed by a delayed elastic deformation. Comparison of the results obtained for different bacterial strains suggests that the instantaneous elastic response might be dominated by the properties of the peptidoglycan layer of the cells and the nature of its association with the membranes, whereas the delayed elastic response is more likely to arise from the liquid-like character of the cell membranes. In the second part, the influence of surface topography on bacterial adhesion is evaluated by means of spatially organized microtopographic surface patterns. The results obtained demonstrated that bacterial cells actively select their initial position to settle on these surfaces. In particular, it was found that cells readily favor those geometrical locations on which the established contact points with the surface is maximized, i.e. the square corners and convex walls of recessed surface features rather than the flat or concave walls of equal protruding features. It was further shown that all surface patterns investigated provoked a significant reduction in bacterial adhesion (4095 % ) and biofilm formation (2258 %), demonstrating that engineered surface topographies, in the absence of chemical and biological modifications, provide a novel and successful approach to inhibiting bacterial adhesion and biofilm formation.