An effective bacteriocin was identified and characterized. Lactic acid bacteria were screened against Campylobacter jejuni. One bacteriocin producer, Enterococcus faecium (NRRL B-30746), was studied. The isolate was grown, and the bacteriocin was purified to single-band homogeneity. Biochemical traits indicated that the peptide was a Class IIa bacteriocin, and it was named E 50-52. The bacteriocin had a molecular weight of 3339.7 and an isoelectric point of 8.0. The minimal inhibitory concentrations of E 50-52 against C. jejuni, Yersinia spp., Salmonella spp., Escherichia coli O157:H7, Shigella dysenteriae, Morganella morganii, Staphylococcus spp., and Listeria spp. ranged from 0.025 to 32 microg/mL. In therapeutic broiler trials, oral treatment with E 50-52 reduced both C. jejuni and Salmonella enteritidis by more than 100,000-fold in the ceca, and systemic S. enteritidis was reduced in the liver and spleen. The wide range of antibacterial activity of bacteriocin E 50-52 against pathogens provides a promising alternative to antibiotics.