**Core Concept**
Antimicrobial drug synergism occurs when two or more drugs, used in combination, produce a greater antimicrobial effect than the sum of their individual effects. This concept is crucial in the treatment of severe infections, particularly in cases where resistance patterns are a concern.

**Why the Correct Answer is Right**
Established antimicrobial drug synergisms involve combinations that target different aspects of microbial growth and replication. For example, the combination of ampicillin and sulbactam (a beta-lactamase inhibitor) synergizes by overcoming bacterial resistance to beta-lactam antibiotics. Similarly, the combination of aminoglycosides and beta-lactams synergizes by inhibiting protein synthesis and cell wall synthesis, respectively. Another example is the combination of polymyxin B and rifampicin, which synergizes by inhibiting cell membrane function and DNA replication, respectively.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not provided, but assuming it's a valid combination, we would need more information to evaluate its synergism.
* **Option B:** This option is not provided, but assuming it's a valid combination, we would need more information to evaluate its synergism.
* **Option C:** This option is not provided, but assuming it's a valid combination, we would need more information to evaluate its synergism.
* **Option D:** This option is not provided, but assuming it's a valid combination, we would need more information to evaluate its synergism.

**Clinical Pearl / High-Yield Fact**
When selecting antimicrobial combinations, it's essential to consider the mechanisms of action, potential synergies, and resistance patterns to optimize treatment outcomes.

**Correct Answer: D.**