Beta-Lactamase (beta-lactam resistance)
Beta-latam antibiotics have a common element in their molecular structure: a four-atom ring known as a beta-lactam. The lactamase enzyme can break that ring open, deactivating the molecule's antibacterial properties.
The beta-lactamases are the major defense of gram-negative bacteria against beta-lactam antibiotics. beta-Lactamases can be broadly divided into enzymes with a serine residue at the active site, similar to bacterial penicillin-binding proteins, from which they probably evolved, and metalloenzymes with zinc ion as a cofactor and with a separate heritage. Both are ancient enzymes. The serine group is estimated from current sequence diversity to have evolved with bacteria over the past 2 billion years.
Here is a list of beta-lactamase types