Which beta-lactam has activity against MRSA?

Which beta-lactam has activity against MRSA?

• A. Cefazolin
• B. Ceftriaxone
• C. Ceftaroline
• D. Piperacillin-tazobactam

Answer: (C)

MRSA resistance comes from a penicillin-binding protein called PBP2a that MRSA expresses; this protein has very low affinity for most beta-lactams, so these drugs can’t effectively inhibit cell wall synthesis. The beta-lactam with activity against MRSA is ceftaroline. It’s a fifth-generation cephalosporin designed to bind PBP2a with high affinity, allowing it to block cell wall synthesis in MRSA and kill the bacteria. The other options lack that capability: cefazolin and ceftriaxone are effective against methicillin-susceptible S. aureus but not MRSA because they don’t bind PBP2a well enough. Piperacillin-tazobactam is broad-spectrum and great for many Gram-negatives and some Gram-positives, but the presence of PBP2a in MRSA keeps it resistant.

MRSA resistance comes from a penicillin-binding protein called PBP2a that MRSA expresses; this protein has very low affinity for most beta-lactams, so these drugs can’t effectively inhibit cell wall synthesis. The beta-lactam with activity against MRSA is ceftaroline. It’s a fifth-generation cephalosporin designed to bind PBP2a with high affinity, allowing it to block cell wall synthesis in MRSA and kill the bacteria. The other options lack that capability: cefazolin and ceftriaxone are effective against methicillin-susceptible S. aureus but not MRSA because they don’t bind PBP2a well enough. Piperacillin-tazobactam is broad-spectrum and great for many Gram-negatives and some Gram-positives, but the presence of PBP2a in MRSA keeps it resistant.