NCIt definition : The sulfate salt form of polymyxin B, a mixture of the polypeptides polymyxins B1
and B2, both obtained from Bacillus polymyxa strains, with antimicrobial activity.
Polymyxin B exerts its antimicrobial effect through its cationic detergent action
on cell membranes. Specifically, this antibiotic binds to the negatively charged site
in the lipopolysaccharide layer of the bacterial cell membrane via electrostatic affinity
with the positively charged amino groups in the cyclic peptide portion. Subsequently,
the fatty acid portion of polymyxin B dissolves in the hydrophobic region of the bacterial
cell membrane. This results in an alteration in cell membrane structure, disruption
of cell wall integrity and an increase in permeability for water and molecules. This
will eventually lead to bacterial cell death.;