Table 2.

Imipenem-hydrolyzing activities of crude extracts ofP. aeruginosa VR-143/97 and of the two E. coli clones (DH5α[pAC2AL] and DH5α[pAC2IL]) able to grow on imipenem-containing mediuma

StrainSp act (pmol/min/μg of protein)b
Crude extractCrude extract + EDTACrude extract + EDTA + Zn2+ c
VR-143/97109 ± 615 ± 1 (14)112 ± 7 (103)
DH5α(pAC2AL)512 ± 2040 ± 3 (8)493 ± 21 (96)
DH5α(pAC2IL)489 ± 2038 ± 3 (8)481 ± 23 (98)
  • a The basal activity measured withE. coli DH5α containing the empty vector is also reported for comparison. Specific activity data represent the mean ± standard deviations of three measurements.

  • b Numbers in parentheses represent the percent activity measured after exposure to EDTA or subsequent Zn2+addition, considering as 100% the activity of the crude extract. See Materials and Methods for experimental details.

  • c The addition to crude extracts untreated with EDTA of Zn2+ at the same concentration used for the enzyme reactivation assay caused an increase (approximately 1.5-fold) in the carbapenemase activity. Zn2+ alone at the same concentration did not cause any detectable hydrolysis of the substrate.

  • d NA, not assayed.