TABLE 1

Cell-based assays to determine MIC values of E. coli DH10B expressing blaPenI and the C69X variants of PenI for selected β-lactams and β-lactam–β-lactamase inhibitor combinations

StrainMICa (mg/liter)
AMPTHINTAXCAZAZTIMIAMP-CLAVbAMP-SULbPIP-TAZOc
E. coli DH10B pBC SK(+)420.060.2510.550/0.0650/12/0.25
E. coli DH10B pBC SK(+) blaPenId5122564280.2550/0.0650/44/0.5
C69A5125122410.2550/0.12550/44/0.5
C69D840.1250.510.2550/0.0650/14/0.5
C69E8161410.2550/0.0650/14/0.5
C69F81646410.2550/0.0650/14/0.5
C69G256640.25210.2550/0.12550/28/1
C69H646421610.2550/0.0650/14/0.5
C69I256320.51610.2550/0.0650/18/1
C69K81611610.2550/0.0650/14/0.5
C69L5121280.5410.550/0.0650/48/1
C69 M25625621610.550/0.0650/14/0.5
C69N2561280.5810.550/0.0650/28/1
C69P420.060.2510.2550/0.0650/12/0.25
C69Q641611610.2550/0.0650/14/0.5
C69R8811610.2550/0.0650/14/0.5
C69S256320.1250.510.550/0.0650/48/1
C69T5122560.5110.550/0.0650/416/2
C69V512640.5810.550/0.2550/48/1
C69W480.1250.510.2550/0.0650/12/0.25
C69Y41686410.2550/0.0650/14/0.5
  • a β-Lactam and β-lactamase inhibitor abbreviations: AMP, ampicillin; THIN, cephalothin; TAX, cefotaxime; CAZ, ceftazidime; AZT, aztreonam; IMI, imipenem; CLAV, clavulanic acid; SUL, sulbactam; and TAZO, tazobactam. Experiments were completed in triplicate. Elevated CAZ MICs are in boldface.

  • b AMP was maintained at a constant concentration of 50 mg/liter, and the clavulanic acid and sulbactam concentrations were varied.

  • c Piperacillin and tazobactam were varied at a ratio of 8:1.

  • d All of the C69 variants were expressed from pBC SK(+) blaPenI in E. coli DH10B.