Table 1.

MICs of β-lactam antibiotics for strains producing CTX-M-4 wild-type and S237A mutant β-lactamases

AntibioticMIC (μg/ml) for strain (enzyme)
E. coli JM109(pMSL1) (CTX-M-4)E. coli JM109(pMSL1-M) (S237A mutant)E. coli JM109
Ampicillin>512>5124
Amoxicillin-clavulanatea 8324
Ampicillin-sulbactama 321284
Ticarcillin128256<1
Piperacillin256512<1
Piperacillin-tazobactamb 22<1
Cefuroxime512128
Cefotaxime51264<1
Ceftazidime24<1
Aztreonam32128<1
  • a The ratio of penicillin/inhibitor was 2:1.

  • b The inhibitor was used at a fixed concentration of 4 μg/ml.