Purity ~98%; Biological Potency (dry basis): 19600U/mg. Cyclic polypeptide antibiotic produced by Bacillus polymyxa. Complex mixture of at least 30 components, primarily colistin A and B. Colistin (polymyxin E) is a polymyxin antibiotic produced by certain strains of Bacillus polymyxa var. colistinus. Colistin is a mixture of cyclic polypeptides colistin A and B. Colistin is effective against most Gram-negative bacilli and is used as a polypeptide antibiotic. Colistin is a decades-old drug that fell out of favor due to its nephrotoxicity. It remains one of the last-resort antibiotics for multidrug-resistant Pseudomonas aeruginosa, Klebsiella pneumoniae, and Acinetobacter.[1] New Delhi metallo-β-Lactamase multidrug-resistant Enterobacteriaceae have also shown susceptibility to Colistin.[2] Colistin is polycationic and has both hydrophilic and lipophilic moieties. These poly-cationic regions interact with the bacterial outer membrane, by displacing bacterial counter ions in the lipo