The invention pertains to an antimicrobial preparation directed against Gram-negative bacteria comprising at least two amino acids chosen from at least one of group I, group II, and group III, wherein group I is the group of neutral amino acids consisting of glycine and alanine, group II is the group of hydroxy-containing amino acids consisting of serine and threonine, and group III is the group of basic amino acids consisting of arginine, lysine, and ornithine, or directed against Listeria monocytogenes comprising the combination DL-threonine and glycine. The invention further relates to a method for preserving food against bacteria comprising adding to the food said antimicrobial preparations.
