TABLE 1.

β-Lactam MICs for a set of isogenic E. coli strains^a

β-Lactam	MIC(s) (μg/ml) for E. coli strain:
	JC7623 (wild type)	JZM120 (AcrAB−)	AM16 (AmpC−)	AM17 (AcrAB− AmpC−)
Penicillin G	16	8	8	8
Ampicillin	2	1	1	0.5
Amoxicillin	4	4	4	4
Carbenicillin	4	1	4/2	1/0.5
Azlocillin	16	4/2	16	1
Mezlocillin	1	0.03	0.5	0.03
Piperacillin	4	0.25	2	0.25
Cloxacillin	256	2	256	1
Oxacillin	256	0.5	256	0.5
Mecillinam	0.5	0.25	0.5	0.12
Cephalothin	4	4	0.5	0.5
Cefazolin	1	1	0.5	0.5
Cephaloridine	2	1	0.5	0.5
Cefamandole	0.5	0.12/0.06	0.12	0.06
Cefsulodin	16	16	8	8
Cefoperazone	0.03	0.015	0.015	0.0075
Cefuroxime	2	0.12	1	0.12
Cefoxitin	4	1	2	1
Cefmetazole	0.5	0.5	0.5	0.5
Ceftriaxone	0.015	0.015	0.015	0.015
Ceftazidime	0.12	0.12	0.12	0.12
Cefepime	0.0075	0.0075	0.0075	0.0075
Cefpirome	0.015	0.015/0.0075	0.015	0.0075
Imipenem	0.12	0.12	0.12	0.12
Spectinomycinb	16	16	>128	>128
Kanamycinb	4	>128	4	>128
Puromycinc	128	2	128	2
Novobiocinc	32	1	32	1
Erythromycinc	128	8	128	8

^aMIC determination was repeated at least twice. Where different MICs were obtained in different assays, both results are given. 

^bMICs were tested to confirm the presence of interposon units. 

^cGood substrate of the AcrAB pump, used to confirm the absence or presence of the pump.