**Core Concept**
Bacitracin is an antibiotic that belongs to the class of polymyxins, which are naturally occurring compounds produced by certain bacteria. It exerts its antibacterial effect by inhibiting cell wall synthesis in susceptible bacteria.

**Why the Correct Answer is Right**
Bacitracin works by inhibiting the dephosphorylation of bactoprenol, a molecule involved in the transfer of peptidoglycan subunits across the cell membrane. This inhibition prevents the formation of a stable peptidoglycan layer in the bacterial cell wall, ultimately leading to cell lysis and death. Bacitracin is most effective against Gram-positive bacteria, as it can easily cross the cell membrane and reach the site of action.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because bacitracin is not a type of aminoglycoside antibiotic, which is a different class of antibiotics that inhibit protein synthesis.
**Option B:** Incorrect because bacitracin is not primarily used as an antifungal agent; its primary use is as an antibacterial agent.
**Option C:** Incorrect because bacitracin is not a type of beta-lactam antibiotic, which includes penicillins and cephalosporins that inhibit cell wall synthesis by a different mechanism.

**Clinical Pearl / High-Yield Fact**
Bacitracin is often used topically in ophthalmic and dermatological preparations due to its ability to inhibit bacterial growth on the skin and mucous membranes.

**Correct Answer:** D. Bacitracin is a polymyxin antibiotic that inhibits cell wall synthesis in susceptible bacteria.