To combat the rise of foodborne disease outbreaks in fresh and ready-to-eat (RTE) meats and to reduce further bacterial drug resistance, researchers are looking to natural and chemical alternatives to antibiotics. These alternatives include, but are not limited to, plant and herbal extracts, vaccines, and bacterial proteins. One alternative, bacteriocins, are being used in livestock production, food manufacturing and processing, and retail packaging and sanitization. Bacteriocins are proteinaceous compounds produced by and lethal to bacteria of species similar to the producing strain. Various bacteriocins---including nisin, colicin, pediocin, cloacin, and lactic acid bacterial peptides---have been evaluated for use in food products or animal production as antibacterial strategies. Colicins, specifically, are produced by certain strains of Escherichia coli and like species. Bacteriocins within the colicin family have been shown to have several different killing mechanisms including pore-formation, nuclease activity against the DNA and RNA of target cells, as well as inhibition of protein synthesis. Work presented in this dissertation involves the use of colicin E1, a pore-forming colicin, against E. coli O157:H7, as well as the first documented antimicrobial efficacy of colicin E1 against the gram-positive pathogen Listeria monocytogenes. Colicin E1 provided powerful reduction of E. coli O157:H7 as a beef carcass spray intervention. Further testing with this bacteriocin demonstrated its unexpected inhibitory activity against the gram-positive pathogen Listeria monocytogenes. The mechanism of action of colicin E1 against L. monocytogenes was investigated using flow cytometry, spectrophotmetric leakage assays, and both light and transmission electron microscopies. Colicin E1 had direct affinity to several L. monocytogenes proteins. These proteins were discovered using affinity chromatography and identified using MALDI-TOF. These colicin E1-binding proteins included DNA polymerase III, LepA, and a cell wall anchor family protein. At this point, there is no literature stating any colicin having interaction with these proteins, suggesting Colicin E1 exerts its antimicrobial activity against L. monocytogenes in an independent and novel fashion.