Bacitracin

Bacitracin<ref>Template:Cite book</ref> is a polypeptide antibiotic. It is a mixture of related cyclic peptides produced by Bacillus licheniformis bacteria, that was first isolated from the variety "Tracy I" (ATCC 10716) in 1945.<ref>Originally grouped under B. subtilis, but nomenclature has since changed. See Template:Cite web</ref> These peptides disrupt Gram-positive bacteria by interfering with cell wall and peptidoglycan synthesis.

Bacitracin is primarily used as a topical preparation, as it can cause kidney damage when used internally.<ref name="Zintel">Template:Cite journal</ref> It is generally safe when used topically, but in rare cases may cause hypersensitivity, allergic or anaphylactic reactions, especially in people allergic to neomycin.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref>

In 2023, it was the 323rd most commonly prescribed medication in the United States, with more than 100,000 prescriptions.<ref>Template:Cite web</ref>

Medical uses

A squeeze tube of bacitracin ointment for the eye

Bacitracin is used in human medicine as a polypeptide antibiotic and is "approved by the US Food and Drug Administration (FDA) for use in chickens and turkeys," though use in animals contributes to antibiotic resistance.<ref name="disc">Template:Cite web</ref>

As bacitracin zinc salt, in combination with other topical antibiotics (usually polymyxin B and neomycin) as an ointment ("triple antibiotic ointment," with the brand name Neosporin), it is used for topical treatment of a variety of localized skin and eye infections, as well as for the prevention of wound infections. A non-ointment form of ophthalmic solution is also available for eye infections.<ref>Template:Cite web</ref>

3D Chemical Structure of Bacitracin

Spectrum of activity and susceptibility data

Bacitracin is a narrow-spectrum antibiotic. It targets Gram-positive bacteria, especially those that cause skin infections. The following represents susceptibility data for a few medically significant microorganisms.<ref>Template:Cite web</ref>

• Staphylococcus aureus – ≤0.03 μg/mL – 700 μg/mL
• Staphylococcus epidermidis – 0.25 μg/mL – >16 μg/mL
• Streptococcus pyogenes – 0.5 μg/mL – >16 μg/mL

Mechanism of action

Template:Main Bacitracin interferes with the dephosphorylation of C₅₅-isoprenyl pyrophosphate, and a related molecule known as bactoprenol pyrophosphate; both of these lipids function as membrane carrier molecules that transport the building-blocks of the peptidoglycan bacterial cell wall outside of the inner membrane.<ref name="pmid4332017">Template:Cite journal</ref>

History

Bacitracin was isolated by Balbina Johnson, a bacteriologist at the Columbia University College of Physicians and Surgeons.<ref name="pmid17770204"/> Its name derives from the fact that a compound produced by a microbe in young Margaret Tracy's (1936–1994)<ref>Template:Cite web</ref> leg injury showed antibacterial activity.<ref>Template:Cite web</ref>

"One strain isolated from tissue debrided from a compound fracture of the tibia was particularly active. We named this growth-antagonistic strain for the patient, Tracy I. When cell-free filtrates of broth cultures of this bacillus proved to possess strong antibiotic activity and to be non-toxic, further study seemed warranted. We have called this active principle 'bacitracin'."<ref name="pmid17770204">Template:Cite journal</ref>

Bacitracin was approved by the US FDA in 1948.<ref>Template:Cite web</ref>

Synthesis

Bacitracin is synthesised via nonribosomal peptide synthetases (NRPSs), which means that ribosomes are not directly involved in its synthesis. The three-enzyme operon is called BacABC, not to be confused with BacABCDE of bacilycin synthesis.<ref>Template:Cite journal</ref>

Composition

Bacitracin is composed of a mixture of related compounds with varying degrees of antibacterial activity. Notable fractions include bacitracin A, A1, B, B1, B2, C, D, E, F, G, and X.<ref>"Committee for Veterinary Medicinal Products Bacitracin." Ema.europa.eu. The European Agency for the Evaluation of Medicinal Products, June 1998. Web. 18 January 2013</ref> Bacitracin A has been found to have the most antibacterial activity. Bacitracin B1 and B2 have similar potencies and are approximately 90% as active as bacitracin A.<ref name="pmid1601975">Template:Cite journal</ref>

Society and culture

Controversies

Claims that bacitracin is a protein disulfide isomerase inhibitor are disputed by in vitro studies.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref>