Serratia marcescensN28b produces bacteriocin 28b, active againstEscherichia coli. Bacteriocin sensitivity tests performed on a collection ofE.colienvelope mutants, and isolation and characterization ofE.colibacteriocin-28b-insensitive mutants, showed that the core lipopolysaccharide, outer membrane proteins OmpA and OmpF, and TolQ, TolA, and TolB proteins are involved in bacteriocin 28b lethal activity. These mutants were assayed for bacteriocin 28b sensitivity under normal and bypass conditions, and their bacteriocin-binding ability was determined. The results obtained suggest that the core lipopolysaccaride and outer membrane proteins OmpA and OmpF are involved in bacteriocin 28b binding. Furthermore, bacteriocin 28b translocation requires proteins TolA, TolB, and TolQ.Key words: bacteriocin, receptors, translocation,Serratia marcescens.