This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
[{'content': "Which of the following is not a mechanism for resistance to MRSA - \nSelect and explain. \nA. Resistance is chromosomally mediated, B. Produced mainly by alteration in PBP's, C. MRSA resistance is absolutely beta lactamase dependent, D. Intrinsic resistance is known", 'role': 'user'}, {'content': 'Answer: C \nExplanation: In the previous explanation, I have explained the mechanism of antibiotic resistance in general (for all staphylococci species).\nAntibiotic resistance specific to MRSA:-\n\nMechanism of resistance of MRSA \n\nThere are three known mechanisms for which Staphylococcus aureus become resistant to methicillin:-\n\n\nPresence of penicillin-binding protein (PBP 2a) → Most cases\nModification of normal (intrinsic) penicillin-binding protein\nHyperproduction of beta-lactamase → rare\n\n\nS. aureus strains have four intrinsic penicillin-binding proteins (PBPs) which have a high affinity for beta-lactam antibiotics.\nPBP2a is an inducible acquired protein that is produced only by MRSA; it is not an intrinsic PBP.\nPBP2a has a very low affinity for beta-lactam antibiotics → S.aureus strains containing PBP2a i.e.MRSA are resistant to all beta-lactam antibiotics\n\n\nProduction of PBP2a is chromosomally mediated. \n\tNow see each option of question:\n\n\nResistance to MRSA is chromosomally mediated and involves the production of an altered penicillin-binding protein (PBP2a).\nMRSA resistance is not absolutely beta-lactamase dependent. Though altered penicillin-binding protein is involved in most strains, rarely beta-lactamase production is also involved.\nIntrinsic resistance is known, that means an alteration in intrinsic PBPs is also one of the mechanisms for resistance in MRSA. (reminding you PBP2a is not an intrinsic PBP, it is an acquired PBP).', 'role': 'assistant'}]