TABLE 3

Kinetic parameters of CTX-M-14 and CTX-M-140

SubstrateValue of parametera
blaCTX-M-14blaCTX-M-140
Km (μM)Vmax (μM s−1)kcat (s−1)kcat/Km (μM−1 s−1)Km (μM)Vmax (μM s−1)kcat (s−1)kcat/Km (μM−1 s−1)
Ampicillin39.08 ± 14.432.62 ± 0.24197.05 ± 17.985.35 ± 1.2719.19 ± 10.262.55 ± 0.0423.62 ± 0.321.44 ± 0.59
Cephalothin185.14 ± 13.741.19 ± 0.271,116.63 ± 253.836.02 ± 1.19123.61 ± 14.121.23 ± 0.32115.39 ± 31.960.93 ± 0.24
Cefotaxime58.45 ± 15.220.41 ± 0.08761.49 ± 148.5513.54 ± 4.08125.30 ± 21.070.18 ± 0.02343.90 ± 29.232.77 ± 0.26
Ceftazidime223.78 ± 20.040.05 ± 0.0080.90 ± 0.150.004 ± 0.0006NDNDNDND
Cefepime145.97 ± 6.970.02 ± 0.00112.95 ± 0.900.09 ± 0.002NDNDNDND
Aztreonam202.27 ± 40.080.12 ± 0.0111.23 ± 1.280.06 ± 0.008187.74 ± 21.280.35 ± 0.053.23 ± 0.520.02 ± 0.001
  • a Km values are the means for three different measurements ± standard deviations. ND, not determinable.