What does MRSA stand for?

• A. Methicillin-resistant Staphylococcus aureus
• B. Multidrug-resistant Staphylococcus aureus
• C. Methicillin-susceptible Staphylococcus aureus
• D. Methicillin-resistant Streptococcus aureus

Answer: (A)

MRSA denotes a Staphylococcus aureus bacterium that has acquired resistance to methicillin and related beta-lactam antibiotics. This resistance arises because the mecA gene changes the target of these drugs, producing a penicillin-binding protein with very low affinity for beta-lactams, so methicillin and other similar antibiotics no longer effectively kill the bacteria. That’s why this label emphasizes the methicillin resistance specifically, not just a general “multidrug” resistance. The other options miss the key points: one would imply the bacteria are susceptible to methicillin, which isn’t the case; another uses the wrong genus, since the organism is Staphylococcus aureus, not Streptococcus; and the non-specific “multidrug-resistant” phrase doesn’t define the standard acronym MRSA.