Polypeptide antibiotics: bacitracin, colistin, polymyxin b

[Julian]

Polypeptide antibiotics disrupt bacterial cell walls.
Bacitracin is a polypeptide antibiotic that inhibits cell wall synthesis and is active against gram-positive bacteria.
Colistin (polymyxin E) and polymyxin B are cationic polypeptide antibiotics that disrupt the outer bacterial cell membrane by binding to the anionic outer membrane and thereby neutralizing the bacteria’s toxicity and causing bacterial cell death.
Colistin methane sulfonate (colistimethate sodium [CMS]) is a parenteral preparation of a prodrug that is transformed in blood and urine to colistin. CMS is less toxic than colistin.
Polypeptides other than colistin are usually used topically; systemic absorption is negligible.