Polymyxin B is an antibiotic primarily used for resistant
Gram-negative infections. It is derived from the bacterium
Bacillus polymyxa. Polymyxin B is composed of a number of related compounds (see "Mixture composition"). It has a bactericidal action against almost all Gram-negative bacilli except the
Proteus and
Neisseria genera. Polymyxins bind to the cell membrane and alter its structure, making it more permeable. The resulting water uptake leads to cell death. Polymyxins are
cationic,
basic peptides that act like detergents (
surfactants). Side effects include neurotoxicity and acute renal tubular necrosis. Polymyxins are used in the topical first-aid preparation
Neosporin.