This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Other topics and Adverse effects, Subject name: Pharmacology
Amoxicillin+clavulanic acid is active against the following organisms EXCEPT: 
Select and explain. 
A. Methicillin resistant Staph. aureus, B. Penicillinase producing Staph. aureus, C. Penicillinase producingN. gonorrhoea, D. b-lactamase producing E.coli
A: Methicillin resistant Staph. aureus
Answer: A: Methicillin resistant Staph. aureus 
Explanation: (Ref: KDT 6/e p702, 703) Staphylococcus aureus develops resistance to methicillin by acquiring altered penicillin binding proteins that have low affinity. No b-lactam antibiotic is effective against MRSA. Clavulanic acid is n inhibitor of b-lactamase. It can restore the sensitivity of penicillins against the organisms who have developed penicillinases.