Four-membered cyclic AMIDES, best known for the PENICILLINS based on a bicyclo-thiazolidine, as well as the CEPHALOSPORINS based on a bicyclo-thiazine, and including monocyclic MONOBACTAMS. The BETA-LACTAMASES hydrolyze the beta lactam ring, accounting for BETA-LACTAM RESISTANCE of infective bacteria.

Synonyms: 0, 4-Thia-1-Azabicyclo(4.2.0)Octanes, beta Lactam, beta-Lactam, beta-Lactams, 4-Thia-1-Azabicyclo(3.2.0)Heptanes, beta Lactams