Antibiotic resistance enzyme. Molecular model of a section of the metallo-beta-lactamase protein fold, a part of metallo-beta-lactamase enzymes. This bacterial enzyme confers antibiotic resistance on cells that carry it. The gene that codes for the enzyme is found on a plasmid, a ring of DNA that is separate to the cell's main DNA, and so can be transferred between cells in close contact. This is possible even if the bacteria do not belong to the same genus. The enzyme inactivates antibiotics in the beta-lactam group, including penicillin and carbapenems, which are the last line of defence used against other drug-resistant bacteria.