Surface of polypropylene (PP) sheets were modified by radiation induced graft polymerization of a mixture of two monomers, a quaternary ammonium salt ([2-(methacryloyloxy)ethyl]-trimethyl ammonium chloride) (QAS) and acrylic acid(AA) to control the bacterial adhesion. Electron beam radiation was used to activate PP sheets prior to the grafting reaction. Depth concentration profile of nitrogen on modified PP up to 10 nm was performed by XPS. However, XPS has revealed no significant changes in the concentration profile of nitrogen for the grafted PP prepared under different parameters. Energetic characteristics (Lifshitz-van der Waals (gamma(LW)), electron acceptor (gamma(+)), and electron donor (gamma(-)) components) of these modified surfaces (with different ratio of comonomer mixtures) were calculated by using contact angle measurements. The PP surfaces prepared under one specific ratio of comonomer mixture (AA : QAS) 20 : 40 (M-4) has been compared with the surfaces modified with 20% AA (AA-20) and 40% QAS (QAS-40). The surface charge and isoelectric point have been determined by zeta potential measurements. AA-20 and comonomer mixture modified PP (M-4) surfaces exhibit negative charges of -27 and -16, respectively, while QAS-40 modified PP surfaces show positive charge of +16. The physicochemical properties of Listeria monocytogenes (LM) were obtained by microbial adhesion to solvent method. Finally, adhesion of LM on unmodified and modified PP surfaces was observed by electron microscopy. (C) 2008 Wiley Periodicals, Inc.