Bacitracin

Bacitracin is a cyclic peptide antibiotic produced by Bacillus subtilis and related Bacillus species. It was discovered in the 1940s and has become a common topical antimicrobial agent, frequently included in over‑the‑counter preparations for minor skin infections.

Its mechanism of action involves interference with bacterial cell wall synthesis. Bacitracin inhibits dephosphorylation of bactoprenol, a lipid carrier that transports peptidoglycan precursors across the cytoplasmic membrane. This disruption prevents proper construction of the cell wall, leading to bacterial death, primarily in Gram-positive organisms.

The antimicrobial spectrum of bacitracin is mainly against Gram-positive bacteria, including Staphylococcus aureus and Streptococcus species. It has limited activity against Gram-negative bacteria because the outer membrane limits drug entry. Bacitracin is not effective systemically for most infections and shows poor oral bioavailability.

Clinical use is predominantly topical or ophthalmic due to nephrotoxicity risk with systemic administration. It is a component of combination products such as triple-antibiotic ointments that include polymyxin B and neomycin, used to prevent infection in minor cuts or abrasions and to protect the ocular surface in some topical preparations.

Adverse effects are primarily local when used topically, including contact dermatitis or allergic reactions. Systemic bacitracin can cause nephrotoxicity and neurotoxicity, so systemic use is limited and closely monitored in specific cases. Resistance to bacitracin exists but is relatively uncommon, arising from altered drug uptake or changes in the target pathway.