Table 2.

MIC and susceptibility data for non-isogenic E. coli isolatesa

Inoculum (CFU/ml) (n) and antibioticMICe (μg/ml)% Susceptibleb,c
 Pip-Tazod 1–322895
 Meropenem0.03– (1/19)
 Cefoteten0.12–1614100 (4/19)
 Cefotaxime2–>1,024256>1,02421 (17/18)
 Ceftazidime4–>1,024>1,024>1,0245 (11/16)
 Ceftriaxone8–>1,0241,024>1,0245 (18/19)
 Cefepime4–>128>128>1285 (18/18)
 Aztreonam4–>1,024>1,024>1,02416 (16/19)
 Pip-Tazo1–1,02481,02458 (8/19)
  • a Excludes isogenic panel of E. coli C600N strains.

  • b Susceptibility based on the percentage of strains inhibited at the NCCLS susceptible breakpoint concentration of each agent. (The breakpoints are only validated for the tests with the 105 CFU/ml inoculum.)

  • c For the inoculum of 107 CFU/ml, in addition to percent susceptibility, the following is shown parenthetically: number of strains showing inoculum effect/number of strains evaluable. (Not all tests were evaluable. For some MICs out of the test range it was impossible to determine if there was an eightfold increase in MIC.)

  • d Pip-Tazo, piperacillin-tazobactam.

  • e 50 and 90%, MICs at which 50 and 90% of isolates are inhibited, respectively.