Table 1.

MICs of cephalosporins and cephalosporins plus β-lactamase inhibitorsa

E. coli isolateMIC (μg/ml) of drug(s) by methodpIβ-Lactamase activityb% β-lactamase inhibition by:
MicrodilutionEtest
CAZFOXCTXCAZFOXFOX-BRLCTXCTX-BRLCLOXcCAd
HUS34/9432>2561664>25624120.25≥947099.61.9
HUS47/9464>2561696>25624160.25≥921599.17.6
HUS36/9464>2561624>2561280.25≥921899.06.3
HUS4/9464>2561664>2561680.25≥934699.18.1
HUS23/9464>25632256e >25696480.38≥9 + 5.4f 2,05732.531.4
HUS42/94128>2563264>25664160.5≥957599.00.6
HUS31/94128>25632256e >25624160.25≥951499.01.9
HUS7/94256>256128256e >2568240.75≥939487.72.6
  • a Abbreviations for cephalosporins: CAZ, ceftzidime; FOX, cefoxitin; CTX, cefotaxime. Abbreviations for β-lactamase inhibitors: CA, clavulanic acid; BRL, BRL 42715. MICs were determined by microdilution or Etest for eight isolates of AmpC-hyperproducing E. coli

  • b Milliunits of enzyme/milligram of protein.

  • c Cloxacillin (250 μM).

  • d Clavulanic acid (2 μM).

  • e Difficult-to-read end-point.

  • f Two β-lactamase bands were detected.