TABLE 3.
Kinetic and inhibition parameters of the A. baumannii AmpC β-lactamasea
| Antibiotic | Km (μM) | Vmax (μmol/ min/μl) | Relative Vmaxb | IC50 (μM) |
|---|---|---|---|---|
| Cephaloridine | 960 | 5,000 | 100 | |
| Ampicillin | 38 | 380 | 7.6 | |
| Ceftazidime | 14 | 52 | 1.0 | |
| Cefotaxime | 7.0 | 25 | 0.5 | |
| Cefoxitin | <1 | <0.01 | ||
| Imipenem | <1 | <0.01 | ||
| Clavulanic acid | 270c | |||
| Sulbactam | 7c | |||
| Tazobactam | 8c |
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.