TABLE 2.

β-Lactam MICs for K. ascorbata, K. cryocrescens, K. georgiana, and E. coli laboratory strains producing representative CTX-M enzymes

β-LactamMIC (μg/ml)
Laboratory E. coli strains producing:Kluyvera strains producing:
CTX-M-3 (77)aCTX-M-15 (77)CTX-M-4 (40)CTX-M-5 (20)CTX-M-9 (14)CTX-M-16 (14)CTX-M-14 (15)CTX-M-27 (15)CTX-M-18 (74)CTX-M-19 (74)CTX-M-8 (17)KLUAb (45)KLUG-1c (78)KLUC-1d (33)
Amoxicillin>512>512>512e>128e>2,048>512>512>512>512>512>5128464
Amoxicillin + CLAf128328328884128128160.51<0.5
Ticarcillin>512>512128>128>512>512>512>512>512>512>5126416128
Ticarcillin + CLA64321281616168256256320.12511
Piperacillin512>512256>128256256256256>512>51222<1
Piperacillin + TZPg242122221680.1250.25<1
Cephalothin>512>5125125125121,024>512>512>512848
Cefuroxime>512>512512512512512512>512>5124416
Cefotaxime512512512>12816161616644160.060.250.06
Cefotaxime + CLA220.060.060.50.50.060.06<0.06
Cefpirome512512222480.12<0.06
Cefepime128640.511644<0.030.12<0.06
Ceftazidime32256216181821281<0.030.12<0.06
Ceftazidime + CLA220.250.250.5160.06<0.06<0.06
Aztreonam1286432128484864480.060.060.06
Aztreonam + CLA0.060.060.250.120.12
Moxalactam0.510.52<0.060.03
Cefoxitin241644410.061
Imipenem0.250.250.50.250.250.250.1250.060.06
  • a Reference numbers are given in parentheses.

  • b Modal MICs for 12 K. ascorbata strains.

  • c MICs for K. cryocrescens.

  • d MICs for K. georgiana.

  • e MIC of ampicillin.

  • f CLA, clavulanate at a fixed concentration of 2 μg/ml.

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