TABLE 1.

MICs of β-lactams and combinations of β-lactams with commercially available β-lactamase inhibitors and penems 1 and 2

Drug or combinationaMIC (mg/liter) for:
K. pneumoniae 1534 blaKPC-2E. coli DH10B (pBR322) blaKPC-2E. coli DH10B
Ampicillin8,1924,0961
Ampicillin-clavulanic acid50/3250/3250/1
Ampicillin-sulbactam50/51250/51250/1
Piperacillin1,0241,0242
Piperacillin-tazobactam512/64512/644/0.5
Piperacillin-penem 116/432/41/4
Piperacillin-penem 232/464/44/4
Cefotaxime1680.06
Cefotaxime-penem 10.25/40.25/40.06/4
Cefotaxime-penem 20.25/40.5/40.06/4
Imipenem880.125
Imipenem-penem 12/42/40.125/4
Imipenem-penem 22/42/40.25/4
  • a In drug combinations, ampicillin was maintained at a constant concentration of 50 mg/liter and clavulanic acid and sulbactam concentrations were increased. For piperacillin-tazobactam, the two components were increased but maintained at a ratio of 8:1. Penem 1 and penem 2 were held at a constant concentration of 4 mg/liter while the concentrations of piperacillin, imipenem, and cefotaxime were increased.