TABLE 6.

Kinetics of growth and production of β-lactamases of E. coli strains XL-1(pLBII-VIM-2) and XL-1(pLBII-VIM-2- W87F), producing the wild-type VIM-2 and the W87F variant, respectivelya

Time (h)E. coli XL-1 (pLBII-VIM-2)E. coli XL-1 (pLBII-VIM-2-W87F)
A600Normalized IPM- hydrolyzing activity (nmol/min·ml)A600Normalized IPM-hydrolyzing activity (nmol/min·ml)
00.10b0.10
0.50.180.18
1.20.320.32
1.70.52300.51
2.30.80390.77
2.81.01100.98
3.31.21701.2
3.81.42401.34.7
4.31.72701.64.7
5.02.03301.87.9
6.02.33802.19.5
  • a The cell concentration in the cultures was estimated by measuring the absorbance at 600 nm (A600). The amount of β-lactamase was estimated as the imipenem-hydrolyzing activity in crude cell extracts normalized to the cell density (see Materials and Methods for details). These results are the means of three independent measurements, and standard deviations were below 10%.

  • b —, imipenem-hydrolyzing activity not detected (≤2.7 nmol/min·ml).