Polymyxin are antibiotics, which disrupt the structure of the bacterial cell membrane, by interacting with its phospholipids. Examples include polymyxins B and E (aka colistin), which are used to Tx Gram negative bacterial infections. The global problem of advancing antimicrobial resistance, has led to a renewed interest in their use. Mattacin is polymyxin M.

• It is a cyclic peptide, with a long hydrophobic tale
• It is produced by nonribosomal peptide synthetase systems in Gram positive bacteria, e.g. Paenibacillus polymyxa, and are selectivelly toxic for Gram negative bacteria, due to their specificcity for the lipopolysaccharide molecule that exists within many Gram negative outer membranes