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: Pharmacology
[{'content': 'Beta-lactam ring is present in all of the following except: March 2008 \nSelect and explain. \nA. Sulbactam, B. Imipenem, C. Vancomycin, D. Cephalexin', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Ans. C: Vancomycin The beta-lactam ring is pa of the structure of several antibiotic families, the principal ones being the penicillins, cephalosporins, carbapenems, and monobactams, which are, therefore, also called beta-lactam antibiotics. These antibiotics work by inhibiting bacterial cell wall synthesis. This has a lethal effect on bacteria, especially on Gram-positive ones.', 'role': 'assistant'}]