Fig. 10
The classification of carbapenemases. Carbapenemases is represented in all classes, A to D, of the Ambler classification system [16]. Functional classification, using the Bush-Jacobi-Medeiros method [17, 18], indicated that the class A carbapenemases were represented by GES and KPC. The β-lactamases belonging to class C, which function as cephalosporinases, are encoded by the AmpC gene carried on the chromosome of many Enterobacteriaceae. ESAC enzymes are known as ESACs. In class D, OXA enzymes, which were originally oxacillinases, have mutated to become CHDLs. Class B β-lactamases are characterized by possessing a metal Zn2+ as the enzyme activity center. IMP- and VIM-type β-lactamases are the main MBLs that fit into the integron structure. MBLs can be classified into three subclasses (B1, B2, B3) based on their amino acid sequence. Subclasses B1 and B3 are characterized by two zinc molecules (Zn1, Zn2) in the enzyme active center, demonstrating more extensive substrate degradation, while subclass B2 has a single Zn2+ at the active center and displays a narrower spectrum