About colistin sulphatea polymyxin antibiotic(mixture of cyclic polypeptides colistin a and b).mechanism of action of colistin sulphatecolistin is a member of poly peptide antibiotic. being poly peptide they exert a detergent like effect. they have high affinity for phospholipids. peptide molecules orient between these phospholipids and cause cell membrane distortion and amino acids and ions come out with in the cell.colistin is useful against gram negative bacteria only.indications for colistin sulphate1.enteric infection 2.systemic infection 3.urinary tract infection