TABLE 3.

Expression of β-lactamase from the norA promoter in transcriptional fusions in E. coli DH5α^a

Plasmid	MICb (μg/ml)	Ratioc	β-Lactamase activityd (u/mg)	Ratio
pWN2018	2	1	1.2 ± 0.4	1
pBF8-30	32	16	17.5 ± 1.7	14
pBF7-7	32	16	17.2 ± 1.5	14

^aCells containing the specified plasmids were grown in LB broth and sonicated prior to determination of β-lactamase activity, which was assayed as specified in Table 2, footnotea. 

^bMIC of ampicillin, determined on Mueller-Hinton agar. 

^cMICs and β-lactamase activities were normalized to that of the strain carrying the vector alone. 

^dβ-Lactamase activities are expressed in units per milligram of proteins and are the means ± standard deviations of at least three determinations.