A diabetic patient developed cellulitis due to S. aureus, which was found to be methicillin resistant after antibiotic sensitivity testing. All of the following antibiotics will be appropriate except
**Core Concept**
Methicillin-resistant Staphylococcus aureus (MRSA) is a type of bacteria that has developed resistance to a broad class of beta-lactam antibiotics, including methicillin and other penicillins. This resistance is primarily due to the acquisition of the mecA gene, which encodes for an altered penicillin-binding protein (PBP2a) with low affinity for beta-lactam antibiotics.
**Why the Correct Answer is Right**
In treating MRSA infections, it is essential to use antibiotics that are effective against this resistant organism. Vancomycin and daptomycin are two such antibiotics that are commonly used to treat MRSA infections. Vancomycin works by inhibiting cell wall synthesis through the binding of the terminal D-alanyl-D-alanine moiety of cell wall precursors, preventing the formation of the peptidoglycan layer. Daptomycin, on the other hand, works by inserting itself into the bacterial membrane, causing cell lysis and death. These antibiotics are effective against MRSA due to their unique mechanisms of action that do not rely on the target of the mecA gene.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because MRSA is often resistant to penicillins, including oxacillin, due to the mecA gene. Oxacillin is a penicillinase-resistant penicillin, but it is still susceptible to the mecA-mediated resistance mechanism.
**Option B:** This option is incorrect because clindamycin can be used to treat MRSA infections, especially in cases where vancomycin is not tolerated. However, it is essential to monitor for clindamycin-induced Clostridioides difficile infection, which can occur due to the disruption of the normal gut flora.
**Option C:** This option is incorrect because trimethoprim-sulfamethoxazole (TMP-SMX) is not typically used to treat MRSA infections. TMP-SMX is more effective against Gram-negative bacteria and is often used to treat urinary tract infections.
**Clinical Pearl / High-Yield Fact**
When treating MRSA infections, it is essential to use antibiotics that are effective against this resistant organism. Vancomycin and daptomycin are two such antibiotics that are commonly used to treat MRSA infections. It is also crucial to monitor for potential side effects, such as nephrotoxicity and Clostridioides difficile infection.
**Correct Answer: B. clindamycin**