Functional amyloid fibers termed curl contribute to bacterial adhesion and biofilm formation in Escherichia coil. We discovered that the nonionic surfactant Tween 20 inhibits biofilm formation by uropathogenic E. coil at the air-liquid interface, referred to as pellicle formation, and at the solid-liquid interface. At Tween 20 concentrations near and above the critical micelle concentration, the interfacial viscoelastic modulus is reduced to zero as cellular aggregates at the air liquid interface are locally disconnected and eventually eliminated. Tween 20 does not inhibit the production of curli but prevents curl-integrated film formation. Our results support a model in which the hydrophobic curli fibers associated with bacteria near the air-liquid interface require access to the gas phase to formed strong physical entanglements and to form a network that can support shear stress.