Abstract
1) Purified samples of polymyxin group antibiotics were shown to be remarkable antimicrobial agents as colistin against E. coli. 2) Removal of the C9-fatty acid from the colistin molecule resulted in the decrease of the activity. 3) The side chain moiety itself showed no antimicrobial activity. 4) The cyclic peptide moiety showed an antimicrobial activity although it was less active than the parent antibiotic. These results indicate that the "active"structure responsible for the antimicrobial activity is the"cyclic peptide moiety"in colistin molecule.
