TABLE 4.

Effects of AmpR mutants against production of class C β-lactamase in E. cloacae ATCC 13047 and three clinical isolates

Plasmid	β-Lactamase activity (U/mg of protein)a
	KU3261	KU3262	KU3263	ATCC 13047
	<0.02	0.06	<0.02	0.07
pKU411	0.02	0.03	<0.02	0.06
pKU412	6.96	6.40	1.72	1.38
pKU413	2.56	2.01	0.34	0.78
pKU415	4.82	4.34	0.93	1.07

^aOne unit of β-lactamase activity was defined as the amount of β-lactamase that hydrolyzed 1 μmol of cephalothin in 1 min at 30°C.