Bacitracin

also known as: Bacitracin Zinc

The topical first-aid antibiotic — one of the most widely used over-the-counter peptide antibiotics, found in virtually every household first-aid kit.

A cyclic polypeptide antibiotic that inhibits bacterial cell wall synthesis by sequestering the C55-isoprenyl pyrophosphate lipid carrier, preventing peptidoglycan recycling — used almost exclusively topically due to nephrotoxicity.

Mechanism of action

Binds to C55-isoprenyl pyrophosphate (undecaprenyl pyrophosphate), the lipid carrier that shuttles peptidoglycan building blocks across the bacterial membrane. By sequestering this carrier, bacitracin prevents its dephosphorylation and recycling, halting cell wall synthesis. Active against gram-positive organisms and some gram-negatives.

Primary uses

Topical wound infection prophylaxis
Minor cuts, scrapes, and burns
Ophthalmic infections (bacitracin ophthalmic ointment)
Surgical irrigation (historically)

Typical dosing

500 units/g (topical ointment) 1–3 times daily (topical) (topical)

Apply thin layer to affected area. Not for deep wounds, animal bites, or serious burns.

Regulatory status

FDA-approved. Available as an over-the-counter topical antibiotic ointment (alone or in Neosporin/triple antibiotic combinations). Oral formulation sometimes used for C. difficile (off-label, rare).

References

[review] Stone KJ, Strominger JL. "Mechanism of action of bacitracin: complexation with metal ion and C55-isoprenyl pyrophosphate." Proc Natl Acad Sci USA, 1971;68:3223-3227.

Related peptides

Polymyxin B

The gram-negative last resort — a cyclic lipopeptide antibiotic revived from the 1950s as a critical weapon against carbapenem-resistant Acinetobacter, Pseudomonas, and Klebsiella.

Daptomycin

A last-resort lipopeptide antibiotic — the first-in-class cyclic peptide that kills MRSA and VRE by depolarizing bacterial membranes, without resistance through traditional mechanisms.

LL-37

The only human cathelicidin — an antimicrobial peptide with direct activity against bacteria, fungi, viruses, and biofilms, with additional roles in wound healing and immune signaling.

Disclaimer

This entry is for educational purposes only and does not constitute medical advice. Dosing information reflects published regulatory or research data and is not a recommendation. Many compounds described here are not approved for human use in the United States. Consult a licensed medical professional before considering any peptide therapy.