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.It is commercially available as 'Coly-monas' (India, marketed by Glenmark Pharmaceuticals ltd)

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.

NDM-1 metallo-β-lactamase multidrug-resistant Enterobacteriaceae have also shown susceptibility to Colistin.