TABLE 1.

MICs of β-lactams for M. morganii clinical isolates, derived AmpC hyperproducers, and E. coli strains harboring ampC from M. morganii

Antibiotic(s)	MIC (μg/ml) for:
	Wild-type strains			AmpC hyperproducers			Escherichia coli strains
	PP19	PP29	PP37	PP19C	PP29II	PP37B	TCR192c	TC192-2d	Top10 F′
Ampicillin	256	64	32	1,024	1,024	512	512	256	2
Ampicillin-clavulanatea	128/64	128/64	64/32	512/256	512/256	256/128	256/128	128/64	2/1
Piperacillin	16	0.25	0.25	>64	32	16	64	32	1
Piperacillin-tazobactamb	1	0.063	0.063	32	8	4	16	8	0.5
Cephalothin	>512	>512	>512	>2,048	>2,048	>2,048	>512	256	2
Cefoxitin	32	8	4	64	16	64	64	16	2
Cefotaxime	≤0.032	≤0.032	≤0.032	16	4	16	2	0.5	≤0.032
Ceftazidime	1	0.5	0.5	32	16	64	8	4	0.063
Cefoperazone	1	1	2	32	8	16	0.25	0.25	≤0.032
Cefepime	≤0.008	≤0.008	≤0.008	≤0.008	≤0.008	≤0.008	0.008	0.016	0.016
Imipenem	2	2	2	2	2	1	2	2	0.063
Aztreonam	≤0.032	≤0.032	≤0.032	0.5	0.5	0.064	0.5	0.5	0.063

^aUsed at a ratio of 2:1.

^bFixed concentration of 4 μg/ml.

^cStrain harboring pMCR19-2 (ampC, ampR from M. morganii strain PP19).

^dStrain harboring pMC192-2 (ampC from M. morganii strain PP19).