Table 3.

Kinetic and inhibition parameters of the A. baumannii AmpC β-lactamasea

AntibioticKm (μM)Vmax(μmol/ min/μl)Relative VmaxbIC50 (μM)
Cephaloridine9605,000100
Ampicillin383807.6
Ceftazidime14521.0
Cefotaxime7.0250.5
Cefoxitin<1<0.01
Imipenem<1<0.01
Clavulanic acid270c
Sulbactam7c
Tazobactam8c
  • a Kinetic experiments were performed using a 7.45-mg/ml proteic extract with a specific activity of 0.064 μmol of nitrocefin hydrolyzed/min/μg of protein.

  • b Obtained by normalizing the value for each antibiotic to that for cephaloridine (set to 100).

  • c Nitrocefin (25 μg/ml) was used as the substrate following 10 min preincubation of enzyme and inhibitor.