Bacitracin is a mixture of polypeptide antibiotics pro-duced by Bacillus subtilis. As with penicillin, it contains a thiazolidine nucleus attached through L-leucine to a pep-tide composed of both D- and L-amino acids. However, it does not contain a β-lactam ring. Bacitracin prevents cell wall synthesis by binding to a lipid pyrophosphate carrier that transports cell wall precursors to the growing cell wall.
Bacitracin inhibits the dephosphorylation of this lipid carrier, a step essential to the carrier molecule’s ability to accept cell wall constituents for transport.
Bacitracin inhibits gram-positive cocci, including Staphy-lococcus aureus, streptococci, a few gram-negative or-ganisms, and one anaerobe, Clostridium difficile.
Bacitracin is primarily a topical antibiotic. Previously, it was administered intramuscularly, but the toxicity asso-ciated with its parenteral administration has precluded systemic use. The bacitracins are not absorbed from the gastrointestinal tract following oral administration.
Bacitracin is highly active against staphylococci, Strep-tococcus pyogenes, and C. difficile. Its high degree of activity against the group A streptococci is used in the laboratory as a means of differentiating between the Lancefield group A streptococci and other streptococci.
Bacitracin is well tolerated topically and orally and is frequently used in combination with other agents (notably polymyxin B and neomycin) in the form of creams, ointments, and aerosol preparations. Hydro-cortisone has been added to the combination for its an-tiinflammatory effects. Bacitracin preparations are ef-fective in the treatment of impetigo and other superficial skin infections. However, poststreptococcal nephritis has followed the topical treatment of im-petigo, and therefore oral penicillin therapy is pre-ferred. Bacitracin has been used with limited success for eradication of S. aureus in the nares. Because of the risk of serious nephrotoxicity, the parenteral use of baci-tracin is not justified.