Table 2.

β-Lactam MICs for CTX-M-9- and CTX-M-16-producingE. coli DH5α

β-LactamMIC (μg/ml) for E. coliDH5α with:
PCPRio-6a CTX-M-16pCPRio-7b CTX-M-9pBK-CMV
Amoxicillin>2,048>2,0482
Amoxicillin + CLAc 882
Ticarcillin>2,048>2,0482
Ticarcillin + CLAc 16162
Piperacillin2562562
Piperacillin + TZBd 222
Cephalothin5125124
Cefuroxime512512<2
Cefotaxime16160.06
Cefotaxime + CLAc 0.060.060.06
Cefotaxime + TZBc 0.060.060.06
Cefotaxime + SULc 0.5020.06
Aztreonam840.12
Aztreonam + CLAc 0.060.060.06
Aztreonam + TZBc 0.060.060.12
Aztreonam + SULc 0.250.500.12
Ceftazidime810.12
Ceftazidime + CLAc 0.250.250.12
Ceftazidime + TZBc 0.250.250.12
Ceftazidime + SULc 0.500.500.12
Cefpirome220.06
Cefpirome + CLA0.060.060.06
Cefpirome + TZBc 0.060.060.06
Cefpirome + SULc 0.250.500.06
  • a E. coli DH5α harboring recombinant plasmid pCPRio-6, which encodes β-lactamase CTX-M-16.

  • b E. coli DH5α harboring recombinant plasmid pCPRio-7, which encodes β-lactamase CTX-M-9.

  • c CLA, clavulanate; TZB, tazobactam; SUL, sulbactam at fixed concentration of 2 μg/ml.

  • d TZB at fixed concentration of 4 μg/ml, as in the commercially available combination with piperacillin.