Nanopillars have been shown to mechanically damagebacteria, suggesting a promising strategy for future antibacterial surfaces.However, the mechanisms underlying this phenomena remain unclear, whichultimately limits translational potential toward real-world applications. Usingreal-time and end-point analysis techniques, we demonstrate that in contrastto initial expectations, bacteria on multiple hydrophilic“mechano-bactericidal”surfaces remained viable unless exposed to a moving air−liquidinterface, which caused considerable cell death. Reasoning that normal forcesarising from surface tension may underlie this mechano-bactericidal activity,we developed computational and experimental models to estimate,manipulate, and recreate the impact of these forces. Our experimentstogether demonstrate that a critical level of external force acting on cellsattached to nanopillar surfaces can rapidly deform and rupture bacteria.These studies provide fundamental physical insight into how nanopillarsurfaces can serve as effective antibacterial materials and suggest use-conditions under which such nanotechnology approaches mayprovide practical value.