Colistin sulfate is a polypeptide antibiotic which penetrates into and disrupts the bacterial cell membrane. It is a cyclic polypeptide antibiotic from Bacillus colistinus. It is composed of Polymyxins E1 and E2 (or Colistins A, B, and C). Colistin was first isolated in Japan in 1949 from a flask of fermenting Bacillus polymyxa var. colistinus and became available for clinical use in 1959. The following local adverse events have been reported with topical corticosteroids, especially under occlusive dressings: burning, itching, irritation, dryness, folliculitis, hypertrichosis, etc. Healthcare providers had largely stopped using colistin in the 1970s because of its toxicity. However, with antibacterial resistance on the rise, colistin is increasingly being used today to treat severe, multidrug-resistant Gram-negative bacterial infections, particularly among intensive care-based patients. The problem with re-introducing an older drug, such as colistin, though, is that techniques for evaluating new drugs have evolved since the 1950s, and therefore, little is known about the dose needed to effectively fight infection while limiting the potential emergence of antimicrobial resistance and reducing potentially toxic side effects. More data are needed to guide optimal use of these older medications. An international team of NIAID-funded researchers is making progress in obtaining better dosing information about colistin and how best to use the antibiotic to treat Gram-negative bacterial infections. Resistance to colistin is rare. The first colistin-resistance gene that is carried in a plasmid and can be transferred between bacterial strains was described in 2016. This plasmid-borne mcr-1 gene has since been isolated in China, Europeand the United States.