The bacterial anti adhesive properties of polysulfone (PSU) microfiltration membranes modified with poly(allylamine hydrochloride) (PAH)/poly(acrylic acid) (PAA) polyelectrolyte multilayers (PEMs) were investigated in this study. Using a direct microscopic observation membrane filtration system, the deposition kinetics of Escherichia coli cells on the membrane surfaces, as well as the reversibility of bacterial deposition, were examined in the absence and presence of calcium. The PEM-modified membranes exhibited significantly improved bacterial anti adhesive properties compared to the PSU base membranes in both the rested solution chemistries. Specifically, the bacterial deposition kinetics on the modified membranes were slower than the deposition kinetics on the base membranes. Furthermore, the bacterial removal efficiency was significantly enhanced from < 10% to as high as 99% after PEM modification. Interaction force measurements conducted through atomic force microscopy revealed strong, long ranged repulsive interactions between a carboxylare modified latex colloid probe and PEM-modified membranes, while attractive interactions were detected between the colloid probe and PSU base membranes. The bacterial anti adhesive properties exhibited by the PEM-modified membranes were attributed to the highly swollen and hydrated PEMs that inhibit the direct contact or close approach of bacteria to the underlying PSU membranes. (C) 2013 Elsevier B.V. All rights reserved