TABLE 1.

Resistance levels conferred by the parent and hybrid metallo-β-lactamases^a

Plasmid	β-Lactamase	Amino acid residue at position:		MIC (μg/ml) ofb:
		87	196	LOR	CEF	CTX	CAZ	AMP	IMP	ATM
pMS401	IMP-3	Gly	Gly	64	512	64	64	8	1	<0.5
pMS402	Hybrid	Glu	Gly	64	512	64	64	8	1	<0.5
pMS502	Hybrid	Gly	Ser	32	128	32	64	64	2	<0.5
pMS501	IMP-1	Glu	Ser	32	128	32	64	64	2	<0.5
pHSG398 Δ Hd				2	8	<0.5	<0.5	4	<0.5	<0.5
None				2	8	<0.5	<0.5	4	<0.5	<0.5

^aHost strain: E. coli K-12 JM83. 

^bLOR, cephaloridine; CEF, cephalothin; CTX, cefotaxime; CAZ, ceftazidime; AMP, ampicillin; IMP, imipenem; ATM, aztreonam.