any of several toxic antibiotics obtained from a particular soil bacterium

antibiotic produced by Bacillus polymyxin, a soil bacterium.

Polymyxins are cationic detergent antibiotics, with a general structure of a cyclic peptide with a long hydrophobic tail. They disrupt the structure of the bacterial cell membrane by interacting with its phospholipids. Polymyxins have a bactericidal effect on Gram-negative bacilli, especially on pseudomonas and coliform organisms.