Cereins are a group of bacteriocins produced by various strains of the bacterium Bacillus cereus. Although all cereins are by definition produced by B. cereus, it is possible that they are chemically quite different from one another. Cereins have been found to be active against other strains of B. cereus, as well as a broad range of other gram-positive bacteria. Like other bacteriocins, cereins are generally named after the strain in which their production was first discovered. Named cereins include cerein 7, cerein 7B, cerein 8A, and cerein MRX1.