TABLE 2.

Kinetic parameters of purified β-lactamase OXA-58 from A. baumannii MAD compared to those of OXA-40 from A. baumannii CLA-1a

SubstrateOXA-58OXA-40b
kcat (s−1)Km (μM)kcat/Km (mM−1 · s−1)Relative kcat/Kmkcat (s−1)Km (μM)kcat/Km (mM−1 · s−1)Relative kcat/Km
Benzylpenicillin5.550110100523220100
Ampicillin1130875220209
Ticarcillin124048160209
Piperacillin2.55050481235023
Cephalothin0.1150113725023
CefotaximeNDcdND
CeftazidimeND202,500104.5
CefepimeNDND
Cefpirome0.12000.50.5ND
Oxacillin1.57022287630.1
AztreonamNDND
Imipenem0.17.513.5130.16.5157
Meropenem<0.010.075e<0.15<0.7ND
  • a Data are means from three independent experiments. Standard deviations were within 10% of the geometric means.

  • b Data are from reference 18.

  • c ND, no detectable hydrolysis (<0.01 s−1).

  • d —, not determinable

  • e The Ki was determined with benzylpenicillin as the substrate.