TABLE 2.

β-Lactam MICs for E. coli strains

Antibiotica	MIC (μg/ml)
	K-12 J53 TEM-1 (R111)b	XL-1 Bluec	XL-1 Blue TEM-1 (pBSKS)d	XL-1 Blue Asn276Asp (pMBS276D)e
Amx	≥8,192	4	≥8,192	≥8,192
Amx + Clav (2 μg/ml)	64	4	256	2,048
Amx + Tazo (2 μg/ml)	128	4	4,096	≥8,192
Amx + Tazo (4 μg/ml)	64	4	2,048	4,096
Tic	≥8,192	2	≥8,192	≥8,192
Tic + Clav (2 μg/ml)	128	2	256	1024
Tic + Tazo (2 μg/ml)	256	2	≥8,192	≥8,192
Pip	128	0.5	512	256
Pip + Clav (2 μg/ml)	2	0.5	2	8
Pip + Tazo (2 μg/ml)	16	0.5	128	128
Mecillinam	8	0.125	64	32
Cephalothin	16	4	32	16
Cefoxitin	4	2	2	2
Cefotaxime	0.03	≤0.015	≤0.015	≤0.015
Imipenem	0.125	0.125	0.125

^aAmx, amoxicillin; Tic, ticarcillin; Pip, piperacillin; Clav, clavulanic acid; Tazo, tazobactam. 

^bStrain producing TEM-1 (reference strain). 

^cSusceptible recipient strain. 

^dStrain producing TEM-1. 

^eStrain producing TEM-1 with Asp²⁷⁶ substitution.