These are a class of broad-spectrum antibiotics that contain a beta-lactam ring in their molecular structures. This includes penicillin derivatives (penams), cephalosporins(cephems), monobactams, and carbapenems and work by inhibiting cell wall biosynthesis in the bacterial organism. These are the most widely used group of antibiotics. These are used for the prevention and treatment of bacterial infections caused by susceptible organisms. At first, β-lactam antibiotics were mainly active only against Gram-positive bacteria, but recent development of broad-spectrum β-lactamantibiotics active against various Gram-negative organisms has increased their usefulness.