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
Methicillin resistant staphylococci do not respond to b-lactam antibiotics because: 
Select and explain. 
A. They produce a b-lactamase which destroys methicillin and related drugs, B. They elaborate an amidase which destroys methicillin and related drugs, C. They have acquired penicillin binding protein which has low affinity for b-lactam antibiotics, D. They are less permeable to b-lactam antibiotics
C: They have acquired penicillin binding protein which has low affinity for b-lactam antibiotics
Answer: C: They have acquired penicillin binding protein which has low affinity for b-lactam antibiotics 
Explanation: (Ref: KDT 6/e p700) Resistance to most penicillins is due to elaboration of beta-lactamase. Methicillin is most resistant penicilling to b-lactamase. Staphylococcus aureus develops resistance to methicillins by acquisition of altered pencillin binding proteins.