Polymyxin B is an antibiotic primarily used for resistant Gram-negative infections. It is derived from the bacterium Bacillus polymyxa. Polymyxin B is a mixture of two closely related compounds, polymyxin B1 and polymyxin B2. It has a bactericidal action against almost all Gram-negative bacilli except the Proteus group. 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 proteins that act like detergents (surfactants). Side effects include neurotoxicity and acute renal tubular necrosis. Polymyxins are used in the topical first-aid preparation Neosporin.
Family of polypeptides with attached fatty acid; cationicdetergent at physiological pH, both hydrophilic and hydrophobic properties
Alters bacterial outer membrane permeability by binding to a negatively charged site in the lipopolysaccharide layer, which has an electrostatic attraction for the positively charged amino groups in the cyclic peptide portion (this site normally is a binding site for calcium and magnesium counter ions); the result is a destabilized outer membrane
Fatty acid portion dissolves in hydrophobic region of cytoplasmic membrane and disrupts membrane integrity
Leakage of cellular molecules, inhibition of cellular respiration
In addition to its antibiotic function, polymyxin B has been used to clear endotoxin contamination in reagents. Polymyxin B is also used to induce envelope stress in order to study the organisms response to such stress. Polymyxin envelope stress assays such as this have been used for the study of sRNA responses in Salmonella enterica.