Which statement is true regarding vancomycin's activity?

• A. It is effective against MRSA
• B. It is effective against Gram-negative rods only
• C. It treats viral infections
• D. It is a beta-lactam

Answer: (A)

Vancomycin is a glycopeptide antibiotic that targets cell wall synthesis in Gram-positive bacteria by binding to the D-Ala-D-Ala terminus of peptidoglycan precursors, thereby blocking cross-linking and production of a strong cell wall. This mechanism makes it bactericidal against organisms with thick peptidoglycan layers, including MRSA, which is resistant to many beta-lactam antibiotics. That’s why it’s effective for MRSA infections. It’s not active against most Gram-negative rods because the outer membrane of these bacteria prevents vancomycin from reaching its target, and its large molecule can’t rely on porins to gain entry. It does not treat viral infections, since antibiotics target bacteria, not viruses. It’s not a beta-lactam; beta-lactams inhibit PBPs with a different mechanism, whereas vancomycin works by binding the D-Ala-D-Ala site on peptidoglycan precursors.