A diabetic patient developed cellulitis due to S. Aureus, which was found to be methicillin-resistant on the antibiotic sensitivity testing. All of the following antibiotics will be appropriate except –
## **Core Concept**
The question tests the understanding of antibiotic resistance, specifically methicillin resistance in *Staphylococcus aureus* (MRSA), and the appropriate antibiotic choices for treating MRSA infections. MRSA is resistant to all beta-lactam antibiotics, including methicillin, due to an alteration in penicillin-binding proteins.
## **Why the Correct Answer is Right**
MRSA infections require antibiotics that are effective against this resistant strain. Common treatments include vancomycin, daptomycin, linezolid, and clindamycin (though resistance rates to clindamycin can vary geographically and by strain). The correct answer will be an antibiotic that is ineffective against MRSA.
## **Why Each Wrong Option is Incorrect**
- **Option A:** Vancomycin is a glycopeptide antibiotic that inhibits cell wall synthesis and is effective against MRSA, making it an appropriate choice.
- **Option B:** Linezolid is an oxazolidinone that inhibits protein synthesis and is used to treat MRSA infections, making it appropriate.
- **Option D:** Daptomycin is a cyclic lipopeptide antibiotic that disrupts multiple aspects of cell membrane functions and is effective against MRSA.
## **Clinical Pearl / High-Yield Fact**
A key point to remember is that MRSA is resistant to all beta-lactam antibiotics (including penicillins, cephalosporins, monobactams, and carbapenems) due to its altered penicillin-binding proteins. Therefore, when treating MRSA infections, one must choose antibiotics that have a different mechanism of action.
## **Correct Answer:** . **Ceftriaxone**