Aztreonam is a synthetic bactericidal monobactam antibiotic. It inhibits bacterial cell wall synthesis by blocking peptidoglycan crosslinking. The inhibition of bacterial cell wall synthesis occurs due to a high affinity of Aztreonam for penicillin binding protein 3 (PBP3). By binding to PBP3, Aztreonam inhibits the third and last stage of bacterial cell wall synthesis. Cell lysis is then mediated by bacterial cell wall autolytic enzymes such as autolysins. It is possible that Aztreonam interferes with an autolysin inhibitor.