Table 2.

Kinetic parameters of CTX-M-9 β-lactamase

Substrate or inhibitorVmaxaIC50(nM)b
Substrates
 Cephaloridine100
 Penicillin48
 Cefotaxime16
 CeftazidimeNCc
 Aztreonam0.1
Inhibitors
 Clavulanic acid10
 Sulbactam700
 Tazobactam1
  • a Relative to that for cephaloridine (which was taken as 100%).

  • b IC50, concentration of β-lactamase inhibitor that inhibits 50% of the activity after 5 min of incubation at 25°C; cephaloridine (0.1 mM) was used as the substrate.

  • c NC, not calculated (rates were to low to obtain reliable values).