Table 1.

MICs of β-lactams for reference and CTX-M-9-producing strains

Antibiotic(s)MIC (μg/ml)
E. coli 785-DaE. coli MSP492bE. coli MSP493cE. coli HB101dE. coli DH5αd
Ampicillin>256>256>2561.51.5
Ampicillin-Sule 1616161.51.5
Amoxicillin-Claf 43411
Ticarcillin>256>256>2561.51
Piperacillin256>256>2560.50.38
Piperacillin-Tazg 30.50.50.750.38
Cefoxitin121.521.51.5
Cefotaxime24>32>320.0320.032
Cefotaxime-Claf 0.190.0320.047≤0.016≤0.016
Ceftazidime11.520.0470.047
Ceftazidime-Claf 0.38≤0.064≤0.064≤0.064≤0.064
Aztreonam264≤0.016≤0.016
  • a Clinical isolate E. coli785-D produces CTX-M-9 along with the TEM-1 penicillinase.

  • b E. coli transconjugant (MSP492).

  • c E. coli DH5α harboring recombinant plasmid pMSP072.

  • d Reference strains.

  • e Sul, sulbactam; the ratio of the penicillin/inhibitor was 2:1.

  • f Cla, clavulanic acid; the ratio of the penicillin/inhibitor was 2:1.

  • g Taz, tazobactam at a fixed concentration of 4 μg/ml.