colistin

co·lis·tin

noun \kə-ˈlis-tən, kō-\

Definition of COLISTIN

: a polymyxin produced by a bacterium of the genus Bacillus (B. polymyxa var. colistinus) and used against some gram-negative pathogens especially of the genera Pseudomonas, Escherichia, Klebsiella, and Shigella