**Core Concept**
Vancomycin is a glycopeptide antibiotic that inhibits cell wall synthesis in Gram-positive bacteria, including multidrug-resistant Staphylococcus aureus. It works by binding to the D-alanyl-D-alanine terminal end of the bacterial cell wall precursor molecule, preventing the incorporation of the molecule into the cell wall.

**Why the Correct Answer is Right**
Vancomycin is the drug of choice for multidrug-resistant Staphylococcus aureus because it has been shown to be effective against strains resistant to other antibiotics, including methicillin-resistant S. aureus (MRSA). Vancomycin's mechanism of action involves the inhibition of cell wall synthesis, which is essential for the growth and survival of bacteria. The binding of vancomycin to the D-alanyl-D-alanine terminal end of the cell wall precursor molecule prevents the incorporation of the molecule into the cell wall, ultimately leading to cell lysis and death.

**Why Each Wrong Option is Incorrect**
**Option A:** Clindamycin is a lincosamide antibiotic that inhibits protein synthesis in bacteria. While it has some activity against S. aureus, it is not the drug of choice for multidrug-resistant strains.
**Option B:** Streptogramins are a class of antibiotics that inhibit protein synthesis in bacteria. They are not typically used as a first-line treatment for multidrug-resistant S. aureus.
**Option D:** Aztreonam is a monobactam antibiotic that inhibits cell wall synthesis in Gram-negative bacteria. It is not effective against S. aureus, regardless of its resistance pattern.

**Clinical Pearl / High-Yield Fact**
Vancomycin is often used in combination with other antibiotics to treat severe S. aureus infections, such as endocarditis or osteomyelitis. It is essential to monitor vancomycin levels in patients receiving this medication to prevent toxicity.

**✓ Correct Answer: C. Vancomycin**