Peptides with antimicrobial properties (AMPs) are produced by eukaryotes and prokaryotes and serve as important components of their defense against microorganisms. Many bacteria are able to synthesize antimicrobial peptides. Those synthesized in the ribosomes, are generally referred to as bacteriocins (antibiotics are not included in the group since they are not ribosomally synthesized). The bacteriocins produced by Gram-negative bacteria are most often large proteins (many are larger that 20 kDa) and their inhibition spectrum is rather narrow, spanning to closely related species. Colicin V and the microcins, are exceptions as they are smaller than 10 kDa.