Table 1.

Classification Schema of β-Lactamase Genes

Ambler Classification	Bush/Jacoby Classification	Notable Enzyme Types
Class A	2a, 2b, 2be, 2br, 2ber, 2c, 2ce, 2e, 2f	ESBLs—TEM, SHV, CTX-M, PER Carbapenemases—KPC
Class B	3a, 3b	Carbapenemases—IMP, VIM, NDM
Class C	1, 1e	Cephalosporinases—AmpC
Class D	2d, 2de, 2df	ESBLs—OXA Carbapenemases—OXA

Source: Bush and Jacoby [2].

Abbreviations: ESBL, extended-spectrum β-lactamase; IMP, active on imipenem metallo-β-lactamase; KPC, Klebsiella pneumoniae carbapenemase; NDM, New Delhi metallo-β-lactamase; OXA, oxacillinase; VIM, Verona integron-encoded metallo-β-lactamase.