Colistin is a polymyxin antibiotic, and 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.

• Storage temperature: +4 °C, desiccate

Mode of Action: Binds to lipids on the cell cytoplasmic membrane of Gram-negative bacteria and disrupts the cell wall integrity.

Antimicrobial spectrum: Gram-negative bacteria. It is proposed that renal reabsorption of colistin may involve organic cation transporters and peptide transporters and that the process is sensitive to pH.

Colistin sulphate is used to permeabilise bacterial cell membranes and to study mannose-resistant haemagglutination and antibiotic resistance in certain organisms, such as A. baumannii. It has been used to study hephrotoxicity in the rat kidney, and MICs, time-kill kinetics, and postantibiotic effect (PAE) against Pseudomonas aeruginosa.