Which antibiotic covers both MRSA and Enterococcus?

Which antibiotic covers both MRSA and Enterococcus?

• A. Vancomycin
• B. Doxycycline
• C. Linezolid
• D. Aztreonam

Answer: (A)

Understanding antibiotic coverage for MRSA and Enterococcus helps explain why vancomycin fits this question. Vancomycin is a glycopeptide that inhibits cell-wall synthesis by binding the D-alanyl–D-alanine terminus of peptidoglycan precursors, a mechanism highly active against Gram-positive organisms. This makes it effective against MRSA and many Enterococcus species that are susceptible to it. It’s a classic choice when a single agent needs to cover both MRSA and non-resistant Enterococcus infections. However, there are vancomycin-resistant Enterococcus strains (VRE), where vancomycin won’t work, so susceptibility testing matters. Other drugs shown don’t reliably cover both pathogens: doxycycline may target some MRSA but Enterococcus is not consistently susceptible; aztreonam targets Gram-negative bacteria, not MRSA or Enterococcus; linezolid does cover both MRSA and Enterococcus (including some VRE) but is not the option highlighted in this question.

Understanding antibiotic coverage for MRSA and Enterococcus helps explain why vancomycin fits this question. Vancomycin is a glycopeptide that inhibits cell-wall synthesis by binding the D-alanyl–D-alanine terminus of peptidoglycan precursors, a mechanism highly active against Gram-positive organisms. This makes it effective against MRSA and many Enterococcus species that are susceptible to it. It’s a classic choice when a single agent needs to cover both MRSA and non-resistant Enterococcus infections. However, there are vancomycin-resistant Enterococcus strains (VRE), where vancomycin won’t work, so susceptibility testing matters.

Other drugs shown don’t reliably cover both pathogens: doxycycline may target some MRSA but Enterococcus is not consistently susceptible; aztreonam targets Gram-negative bacteria, not MRSA or Enterococcus; linezolid does cover both MRSA and Enterococcus (including some VRE) but is not the option highlighted in this question.