Table 1.

MICs of different antibiotics for E. coli97/38582, E. coli MC4100, the E. coli JMG21 (modified MC4100) transconjugant, and E. coli MC4100 with the cloned β-lactamase

Antimicrobial agentMIC (μg/ml) for strain:
97/38582 (clinical strain)aMC4100bJMG21 (transconjugant)bMC4100 (pBctx-M-10)b
103105107
Amoxicillin256256>5124256256
Amoxicillin-clavulanatec 8/48/48/42/14/28/4
Ticarcillin>512>512>5124>512512
Piperacillin64128>51213232
Piperacillin-tazobactamd 1/42/42/41/42/42/4
Cefazolin128512>5124128512
Cefuroxime512512>5122512>512
Cefuroxime plus clavulanatee 224244
Cefpodoxime3232>512≤116256
Cefpodoxime plus clavulanatee ≤1≤1≤1≤1≤12
Cefoxitin448244
Cefotaxime88256≤0.124128
Cefotaxime plus clavulanatee 0.20.250.5≤0.12≤0.120.5
Ceftazidime0.50.510.250.252
Ceftazidime plus clavulanatee ≤0.12≤0.12≤0.12≤0.12≤0.12≤0.12
Aztreonam1264≤0.12216
Cefepime24512≤0.12232
Imipenem≤0.1≤0.12≤0.12≤0.12≤0.120.25
  • a The inoculum effect was tested using 103, 105, and 107 CFU per spot.

  • b At 105 CFU per spot.

  • c 2:1 concentration ratio.

  • d Tazobactam was at a fixed concentration of 4 μg/ml.

  • e Clavulanate was at a fixed concentration of 4 μg/ml.