TABLE 2.

Induction of β-lactamase activity in CMY-13-producing strains

Strain	Cephalosporinase activity (U/mg of protein)a
	Uninduced	Induced	Inducibility (fold)
E. coli DH5α(p541)b	1.04	3.62	3.5
E. coli DH5α(p541, pNH5)b	0.63	0.76	1.2
E. coli DH5α(p541-H)b	2.49	5.05	2.0
E. coli DH5α(p541-HP)	3.19	5.52	1.7
E. coli DH5α	<0.01	NDc

^aOne unit of activity was defined as 1 μmol of substrate hydrolyzed per min. Each value was the mean of three independent measurements not differing more than 10%.

^bExtracts were pretreated with EDTA as described in the text.

^cND, Not determined.