What is "polymyxin"

n. Any of several toxic antibiotics, derived from the soil bacterium ''Bacillus polymyxa'', used to treat infections by gram-negative bacteria

n. any of several toxic antibiotics obtained from a particular soil bacterium

Polymyxins are antibiotics, with a general structure consisting of a cyclic peptide with a long hydrophobic tail. They disrupt the structure of the bacterial cell membrane by interacting with its phospholipids. They are produced by nonribosomal peptide synthetase systems in Gram-positive bacteria such as Paenibacillus polymyxa and are selectively toxic for Gram-negative bacteria due to their specificity for the lipopolysaccharide molecule that exists within many Gram-negative outer membranes.

Polymyxins B and E (also known as colistin) are used in the treatment of Gram-negative bacterial infections. The global problem of advancing antimicrobial resistance has led to a renewed interest in their use recently.

Polymyxin M is also known as "mattacin".