TABLE 2.

Hydrolysis parameters for β-lactamases with low or undetectable carbapenemase activitya

β-LactamaseSubstratekcat (s−1)Km (μM)kcat/Km (s−1 μM−1)Relative kcatRelative kcat/Km
TEM-1Cephaloridine9805601.8100100
Benzylpenicillin1,20012100.01205,600
Imipenem0.00957.20.00130.000970.072
Meropenem0.00023b150.0000150.0000230.00083
Doripenem0.000215.40.0000390.0000210.0022
Ceftazidime0.00232000.0000120.000230.00067
SHV-1Cephaloridine4101602.6100100
Benzylpenicillin1,10016692702,700
Imipenem0.054230.00240.0130.092
Meropenem0.00174.20.000400.000410.015
Doripenem0.00304.30.000700.000730.027
Ceftazidime0.0105000.000020.00240.00077
CTX-M-15Cephaloridine190394.9100100
Benzylpenicillin478.7c5.425110
Imipenem0.171200.00140.0900.029
Meropenem0.004211d0.000380.00220.0078
Doripenem0.00187.10.000250.000950.0051
Ceftazidime4.42400.0182.30.37
K1Cephaloridine4901104.5100100
Benzylpenicillin8004020160440
Imipenem0.091510.00180.0190.040
Meropenem0.0096900.000110.00200.0024
Doripenem0.0068450.000150.00140.0033
Ceftazidime0.0131400.0000930.00270.0021
TEM-26Cephaloridine37660.56100100
Benzylpenicillin765.0152102,700
Imipenem0.0024140.000170.00650.030
Meropenem0.000398.80.0000440.00110.0079
Doripenem0.000378.00.0000460.00100.0082
Ceftazidime951300.73260130
CMY-2Cephaloridine7102902.4100100
Benzylpenicillin222.2103.1420
Nitrocefin1,70040432401,800
Imipenem≤0.031e0.31f0.100.00444.2
Meropenem0.000081e0.060f0.00140.0000110.058
Doripenem0.000072e0.0046f0.0160.0000100.67
Ceftazidime0.00354.50.000780.000490.033
AmpC of P. aeruginosaCephaloridine963500.27100100
Benzylpenicillin44143.1461,100
Nitrocefin150314.81601,800
Imipenem≤0.03e1.6f≤0.019≤0.031≤7.0
Meropenem≤0.006e1.4f≤0.0043≤0.0063≤1.6
Doripenem≤0.006e1.8f≤0.0033≤0.0063≤1.2
Ceftazidime≤0.010e8.0f≤0.0013≤0.010≤0.48
AmpC of E. cloacaeCephaloridine2,500g3307.6100100
Benzylpenicillin324.76.81.389
Imipenem0.012240.000500.000480.0066
Meropenem0.000319.8h0.0000320.0000120.00042
Doripenem0.000439.60.0000450.0000170.00059
Ceftazidime0.0212.90.00720.000840.095
OXA-10iCephaloridine162000.080100100
Benzylpenicillin867.91154014,000
Imipenem≤0.014NDND≤0.088ND
Meropenem≤0.0050NDND≤0.031ND
Doripenem≤0.0073NDND≤0.046ND
Ceftazidime≤0.0095NDND≤0.059ND
  • a Standard deviations were ≤20%, except as noted. Some parameters for selected β-lactamases and comparator substrates were presented as part of a previous study (15). ND, not determined; hydrolysis was too slow to obtain reliable initial rates.

  • b Standard deviation, 0.00005 s−1.

  • c Standard deviation, 3.1 μM.

  • d Standard deviation, 4.3 μM.

  • e Estimated Vmax based on two times the maximum hydrolysis rate observed.

  • f Apparent Ki reported as determined by competitive inhibition of 20 μM nitrocefin.

  • g Standard deviation, 560 s−1.

  • h Standard deviation, 3.0 μM.

  • i Enzyme preparation was ∼50% pure; therefore kcat was not calculated. Vmax is shown in nmol substrate hydrolyzed/min/μg protein; Vmax/Km is presented in place of kcat/Km.