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
Beta-lactam ring is present in all of the following except: March 2008 
Select and explain. 
A. Sulbactam, B. Imipenem, C. Vancomycin, D. Cephalexin
C: Vancomycin
Answer: C: Vancomycin 
Explanation: 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.