<n0:ComplexDefinition xmlns:n0="http://ncicb.nci.nih.gov/xml/owl/EVS/ComplexProperties.xsd#"><n0:def-definition>Compounds containing a four-membered ring with an amide nitrogen and a keto group. This configuration includes bacteriostatic, cell-wall inhibiting antibiotics, such as penicillins and cephalosporins, their analogs and derivatives, such as the penem (or penam) compounds, clavulanic acids, and monobactams. They are substrates for and may act as inhibitors of bacterial beta-lactamases. (MeSH)</n0:def-definition><n0:def-source>NCI</n0:def-source></n0:ComplexDefinition>