NCIt definition : Any of the polymyxin antibiotics, cyclic peptides with long hydrophobic ends, obtained
from Bacillus polymyxa strains. Polymyxin antibiotics exert their antimicrobial effect
through their cationic detergent actions on cell membranes. Specifically, they bind
to the negatively charged site in the lipopolysaccharide (LPS) layer of the bacterial
cell membrane via electrostatic affinity with the positively charged amino groups
in the cyclic peptide portion of the polymyxin antibiotic. Subsequently, the fatty
acid portion of the polymyxin antibiotic dissolves in the hydrophobic region of the
bacterial cell membrane. This results in an alteration in cell membrane structure,
an increase in permeability for water and other molecules and disruption of cell wall
integrity. This leads to bacterial cell death.;