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-b-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 lipopolysaccharide. Hydrophobic/hydrophillic regions interact with the cytoplasmic membrane just like a detergent, solubilizing the membrane in an aqueous environment. This effect is bactericidal even in an isosmolaric environment.
Resistance to colistin is currently rare, but is described. At present there is no agreement about how to look for colistin resistance. The Soci
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