The American Heritage® Dictionary of the English Language, 4th Edition
n. Any of various antibacterial proteins produced by certain strains of the colon bacillus that are lethal to other closely related strains of bacteria.
n. Any of a class of protein, secreted by certain strains of bacteria, that kills but does not lyse other strains.
Word Usage
"This region contains four iron acquisition systems (iutA iucABCD, sitABCD, iroBCDN and temperature-sensitive hemagglutinin tsh), colicin V operon, increasing serum sensitivity iss"