About Piperacillin A semisynthetic extended spectrum penicillin(ureidopenicillin), Antiboitic. Mechanism of Action of Piperacillin Piperacillin is a semi synthetic antipseudomonal Penicillin. It binds to the Penicillin binding protein in the cell wall of bacteria and inhibits the enzyme transpeptidase which is responsible for the transpeptidation reaction in peptidoglycan synthesis. It also activates the endogenous enzyme which degrades the peptidoglycan.These results in inhibition of protein synthesis and there by cell wall synthesis.Piperacillin is active against both gram positive and gram negative organism.