Polypeptides

[Dianne]

Polypeptides are a class of antibiotics used to treat several types of infections. Polypeptides include the following:

Bacitracin
Colistin
Polymyxin B

Most bacteria have an outer covering (cell wall) that protects them. Bacitracin works by preventing bacteria from forming this wall. Colistin and polymyxin B work by disrupting the cell membrane underlying this wall in some bacteria. As a result, the bacteria die.
Bacitracin is used mainly to treat superficial skin infections caused by Staphylococcus aureus. It is applied directly to the skin (topically).
Colistin and polymyxin B commonly cause kidney damage, so they are used only for serious infections in which bacteria are resistant to all other antibiotics and no safer alternatives are available. When colistin or polymyxin B is used, it is given by vein (intravenously). In some cases, colistin may be inhaled through a nebulizer.
(See also Overview of Antibiotics.)