TABLE 1.

MICs of β-lactams conferred in E. coli JM83 by the E. cloacae P99 β-lactamase and its mutants with replacement of Leu-293

Amino acid at res- idue 293	MIC (μg/ml) of indicated β-lactama
	AMP	CAZ	FEP	CRO	CFP	PIP	ATM	LOR
Noneb	4	0.125	<0.015	<0.03	<0.06	0.5	<0.03	4
Leuc	1,024	64	0.5	128	128	128	64	512
Pro	256	256	8	32	128	64	8	64
Gly	512	256	2	64	128	128	16	512
Ala	256	128	2	64	128	128	16	512
Val	512	128	2	64	128	256	32	256
Ser	512	128	2	64	128	128	16	256
Cys	512	128	1	64	64	128	32	256
Asn	512	128	1	32	64	64	32	512
Glu	512	64	1	32	128	128	16	256
Met	512	128	1	128	128	128	32	512
Asp	256	128	2	4	32	8	2	512
Arg	256	32	0.5	64	32	128	64	128
Phe	256	32	0.5	64	128	64	64	256
His	256	16	0.25	32	32	32	64	128
Tyr	256	32	0.25	32	128	32	64	256
Lys	256	32	0.25	64	32	64	64	128

^aAbbreviations: AMP, ampicillin; CAZ, ceftazidime; FEP, cefepime; CRO, ceftriaxone; CFP, cefoperazone; PIP, piperacillin; ATM, aztreonam; LOR, cephaloridine.

^bE. coli JM83 recipient strain.

^cWild-type E. cloacae P99 β-lactamase.