Table 3.

Substrate profile of CTX-M-8 β-lactamase

SubstrateRelativeVmaxaKm (μM)RelativeVmax/Km b
Benzylpenicillin10011100
Amoxicillin371234
Ticarcillin121410
Piperacillin491929
Cephalothin1,07087137
Cefuroxime251223
Cefotaxime49747
Cefpirome3001,2003
Cefepime969901
Aztreonam98000.12
Ceftazidime≤1>500c ≤0.02
CefoxitinNDd 5c
ImipenemND1c
  • a Values are percentages of theV max for benzylpenicillin.

  • b Values are percentages of the relativeV max/Km ratio for benzylpenicillin.

  • c Values were determined asKi by substrate competition with benzylpenicillin.

  • d ND, no catalytic activity detected.