Bacitracin is a complex, cyclical polypeptide with 11 amino acids, isolated from Bacillus subtilis. There are over 15 different bacitracins, but bacitracin A is most potent. Commercial preparations tend to be a mixture of various types. It is used as a production enhancer in the US, and to prevent necrotic enteritis in chickens in NZ but has been banned in Europe.
It binds to isoprenyl phosphate in bacteria and prevents this from synthesising the glycopeptide units (N-acetyl glucuronic acid (NAG) - N-acetyl muraminic acid (NAM) pentapeptide isoprene pyrophosphate) produced for construction of peptidoglycan. Bacitracin thereby inhibits bacterial cell wall synthesis. Divalent cations are required for activity, so bacitracin is often complexed with zinc.
Bacitracin is primarily effective against Gram positive bacteria including some Staphylococcus spp, Streptococcus spp, Haemophilus influenzae, Corynebacterium spp, Neisseria spp, and Clostridium spp. It is not clinically effective against enteric Gram negative bacilli. Its main use is to prevent necrotic enteritis in chickens.
Bacitracin has been around since 1947 and is used by the ton without major resistance developing. Individual farms have problems with resistant Cl perfringens (chromosomally transmitted efflux pump?) which seems to disappear when bacitracin is not used for several batches of chickens. There is a suggestion that bacitracin may cause the expression of high level resistance to vancomycin in enterococci: this is probably not relevant clinically. Politics are a different matter!
Bacitracin complexes with lipids, including those of mammalian cell membranes, and when given systemically is severely nephrotoxic. Therefore, its use is limited to oral or topical application.
Bacitracin is very poorly absorbed orally, and has been used for gastrointestinal sterilisation. There is no withholding time.
It is also used in combination with other drugs in topical preparations, especially those intended for use in ears and eyes.
