This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Systemic Bacteriology Pa 1 (Gram Positive Cocci, Gram Negative Cocci), Subject name: Microbiology
[{'content': 'Which of the following is not mechanism for resistance to MRSA - \nSelect and explain. \nA. Resistance is chromosomally mediated, B. Produced mainly by alteration in PBPs, C. MRSA resistance is absolutely beta-lactamase independent, D. Intrinsic resistance is absent', 'role': 'user'}, {'content': "Answer: C \nExplanation: Option 1, 2 3 mechanisms for which staphylococcus aureus become resistant to methicillin: i) Presence of an acquired penicillin binding protein (PBP2a) ii) Modification of normal (Intrinsic) penicillin binding proteins MRSA is mediated by mecA gene; which is chromosomally coded. iii) Hyperproduction of b-lactamase - Rare Option 3 MRSA resistance is not absolutely b-lactamase independent. Resistance may also be produced by hyperproduction of beta-lactamase. Option 4 Intrinsic Resistance: It is the innate ability of a bacterium to resist a class of antibiotics. S. aureus doesn't show any intrinsic resistance. Enterococci show intrinsic resistance to cephalosporins and cotrimoxazole.", 'role': 'assistant'}]