Methicillin-resistant staphylococci do not respond to β-lactam antibiotics because:
High-Yield Explanation
Resistance to most penicillins is due to elaboration of beta-lactamase.
Methicillin is most resistant penicillin to β-lactamase.
Staphylococcus aureus develops resistance to methicillins by acquisition of altered penicillin binding proteins.