This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: JIPMER 2019, Subject name: Microbiology
[{'content': 'Gene responsible for semisynthetic penicillin resistance in Methicillin resistant Staph aureus (MRSA)? \nSelect and explain. \nA. Mec A, B. Mec B, C. Mec D, D. Mec C', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Methicillin resistance in S. aureus is mediated by a chromosomally coded gene called mec A gene, which alters penicillin-binding protein (PBP) present on S. aureus cell membranetoPBP-2a. * PBP is an essential protein needed for cell wall synthesis of bacteria. Beta lactam drugs bind and inhibit this protein, thereby inhibit the cell wall synthesis. * The altered PBP2a of MRSA strains has less affinity for beta lactam antibiotics; hence, MRSA strains are resistant to all beta lactam antibiotics.', 'role': 'assistant'}]