TABLE 1.

Classification schemes for bacterial β-lactamases, expanded from Bush et al. (16)

Bush-Jacoby group (2009)Bush-Jacoby-Medeiros group (1995)Molecular class (subclass)Distinctive substrate(s)Inhibited byDefining characteristic(s)Representative enzyme(s)
CA or TZBaEDTA
11CCephalosporinsNoNoGreater hydrolysis of cephalosporins than benzylpenicillin; hydrolyzes cephamycinsE. coli AmpC, P99, ACT-1, CMY-2, FOX-1, MIR-1
1eNIbCCephalosporinsNoNoIncreased hydrolysis of ceftazidime and often other oxyimino-β-lactamsGC1, CMY-37
2a2aAPenicillinsYesNoGreater hydrolysis of benzylpenicillin than cephalosporinsPC1
2b2bAPenicillins, early cephalosporinsYesNoSimilar hydrolysis of benzylpenicillin and cephalosporinsTEM-1, TEM-2, SHV-1
2be2beAExtended-spectrum cephalosporins, monobactamsYesNoIncreased hydrolysis of oxyimino-β-lactams (cefotaxime, ceftazidime, ceftriaxone, cefepime, aztreonam)TEM-3, SHV-2, CTX-M-15, PER-1, VEB-1
2br2brAPenicillinsNoNoResistance to clavulanic acid, sulbactam, and tazobactamTEM-30, SHV-10
2berNIAExtended-spectrum cephalosporins, monobactamsNoNoIncreased hydrolysis of oxyimino-β-lactams combined with resistance to clavulanic acid, sulbactam, and tazobactamTEM-50
2c2cACarbenicillinYesNoIncreased hydrolysis of carbenicillinPSE-1, CARB-3
2ceNIACarbenicillin, cefepimeYesNoIncreased hydrolysis of carbenicillin, cefepime, and cefpiromeRTG-4
2d2dDCloxacillinVariableNoIncreased hydrolysis of cloxacillin or oxacillinOXA-1, OXA-10
2deNIDExtended-spectrum cephalosporinsVariableNoHydrolyzes cloxacillin or oxacillin and oxyimino-β-lactamsOXA-11, OXA-15
2dfNIDCarbapenemsVariableNoHydrolyzes cloxacillin or oxacillin and carbapenemsOXA-23, OXA-48
2e2eAExtended-spectrum cephalosporinsYesNoHydrolyzes cephalosporins. Inhibited by clavulanic acid but not aztreonamCepA
2f2fACarbapenemsVariableNoIncreased hydrolysis of carbapenems, oxyimino-β-lactams, cephamycinsKPC-2, IMI-1, SME-1
3a3B (B1)CarbapenemsNoYesBroad-spectrum hydrolysis including carbapenems but not monobactamsIMP-1, VIM-1, CcrA, IND-1
B (B3)L1, CAU-1, GOB-1, FEZ-1
3b3B (B2)CarbapenemsNoYesPreferential hydrolysis of carbapenemsCphA, Sfh-1
NI4Unknown
  • a CA, clavulanic acid; TZB, tazobactam.

  • b NI, not included.