Polymers that directly inhibit the growth of microorganisms at their surface are potentially useful. To investigate the feasibility of such materials, poly(styrene) (PS) resin beads that had had poly(ethyleneglycol) (PEG) grafted onto the surface were further derivatized by covalently linking an antimicrobial peptide onto the surface. The antimicrobial peptide was composed of 8 lysine and 7 leucine (6K8L) residues. The resulting surface-modified polystyrene (SMPS) was microcidal in a concentration and time-dependent manner against several micro-organisms including E. coli O157 : H7, L. monocytogenes, S. aureus, P. fluorescens, and K. marxianus when suspended in phosphate buffer. The SMPS inhibited the growth of pathogenic E. coli O157 : H7 in trypticase soy broth. SMPS was bactericidal at pH 3.5 to 7, retained activity after heating to 200 degreesC for 30 min, and could be extensively washed without loss of antimicrobial activity. Bioassays and HPLC analyses of buffer that had been preincubated with SMPS indicated that antimicrobial activity may have been due, at least in part, to the slow release of a peptide-PEG ligand from the PS to the buffer.