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 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
Polymyxin B is composed of polymyxins B1, B1-I, B2, B3, and B6. Polymyxins B1 and B2 are considered major components. These related components are structurally identical with the exception of a variable fatty acid group on each fraction. Results from in vitro studies have shown marginal differences in MIC data when comparing the fractions.
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.
Polymyxin B has been used to treat urinary tract infections and meningitis caused by Pseudomonas aeruginosa and Haemophilus influenzae, respectively. The following represents MIC susceptibility data for a few medically significant microorganisms.
^Orwa, J. A., et al "Isolation and Structural Characterization of Polymyxin B Components." Isolation and Structural Characterization of Polymyxin B Components 912.2 (2001): 369-73. Sciencedirect. Web. 15 Jan. 2013.