Overview
This lecture discusses bacitracin, including its origins, mechanism of action, spectrum of activity, toxicity, and its common use in topical antibiotic ointments.
Bacitracin Origins & Naming
- Bacitracin is a peptide antibiotic, meaning it is made of short protein chains.
- The antibiotic was originally isolated from Bacillus subtilis found in a wound of a patient named Tracy, which is the source of its name.
Mechanism of Action
- Bacitracin inhibits bacterial cell wall production by blocking the movement of peptidoglycan precursors, not by interfering with their synthesis.
- The drug prevents cell wall components produced inside the cell from being transported to the cell wall.
- A weakened cell wall causes bacterial death due to the inability to withstand osmotic pressure.
Spectrum of Activity & Usage
- Bacitracin is a broad-spectrum antibiotic effective against both Gram-positive and Gram-negative bacteria.
- It is primarily used to treat Gram-positive skin organisms such as Staphylococcus and Streptococcus.
Administration & Toxicity
- Bacitracin can be given orally or intramuscularly but is mainly used topically due to nephrotoxicity (kidney toxicity).
- It is commonly combined with polymyxin B and neomycin in triple antibiotic ointments (e.g., Neosporin).
Key Terms & Definitions
- Peptide antibiotic — antibiotic made of short chains of amino acids (peptides).
- Bacillus subtilis — bacterial species from which bacitracin was first isolated.
- Peptidoglycan — main structural component of bacterial cell walls.
- Nephrotoxic — damaging or toxic to the kidneys.
- Broad-spectrum antibiotic — effective against a wide range of bacteria, including both Gram-positive and Gram-negative strains.
Action Items / Next Steps
- Review the mechanism by which bacitracin blocks cell wall assembly.
- Memorize the three antibiotics included in triple antibiotic ointment: bacitracin, neomycin, and polymyxin B.