Control experiments demonstrate that constant force plateaus and nanospring behaviors originate from type IV pili. Representative forces curves obtained in M63 medium between hydrophobic tips and the polar region of different mutant strains of P. aeruginosa: (a) ΔflgK strain (7% plateau forces and 12% single adhesions; n = 1024 curves), (b) ΔpilA flgK::Tn5 strain (0% adhesion), (c) WT/pPilY1 strain (6% plateau forces and 7% single adhesions), and (d) ΔpilY1 flgK::Tn5 strain (0% adhesion). All curves were obtained using a contact time of 100 ms, a maximum applied force of 250 pN, and approach and retraction speeds of 1.0 μm s–1. Similar data were obtained using three different tips and three cells from different cultures.