Bacitracin ointment is best described as which type of antimicrobial agent?

• A. Cationic polypeptide
• B. Macrolide
• C. Aminoglycoside
• D. Fluoroquinolone

Answer: (A)

Bacitracin is a cationic polypeptide antibiotic that works by blocking cell wall synthesis. It inhibits the dephosphorylation of bactoprenol, the lipid carrier that shuttles peptidoglycan precursors across the cell membrane, so the wall cannot be assembled properly. This mechanism is different from the other classes listed: macrolides inhibit protein synthesis at the 50S ribosome, aminoglycosides disrupt protein synthesis at the 30S ribosome, and fluoroquinolones inhibit DNA gyrase. Because bacitracin targets the cell wall with a positively charged peptide structure, it fits best as a cationic polypeptide antibiotic. It’s used topically largely due to limited systemic absorption and activity mainly against gram-positive bacteria.