Ampicillin

This drug inhibits the bacterial transpeptidase involved in peptidoglycan biosyn­thesis and thus inhibits cell wall biosynthesis (14). As such, ampicillin inhibits log-phase bacteria but not those in a stationary phase. Resistance to ampicillin is conferred by a p-lactamase, which cleaves the p-lactam ring of ampicillin (14). The p-lactamase most commonly expressed by cloning vectors is that encoded by the bla gene (15).