TABLE 2.

In vitro susceptibilities of two clinical E. coli isolates and the E. coli ATCC 25922 control strain determined by the broth microdilution method^a

Antibioticb	MIC (μg/ml)
	ATCC 25922	EC38	EC44
AMP	2	≥64	≥64
AMX + CLA	≤0.25	16	16
CFZ	≤0.25	16	16
FOX	≤0.25	≥64	8
CFX	≤0.25	≥64	16
ATM	≤0.25	8	1
CTR	≤0.25	≤0.5	≤0.5
CTR + CLA	≤0.25	≤0.25	≤0.25
CAZ	≤0.25	4	4
CAZ + CLA	≤0.25	2	2
CTX	≤0.25	2	1
CTX + CLA	≤0.25	1	0.25
IPM	≤0.25	<0.25	<0.25
AMK	≤0.25	4	2
CIP	0.06	2	0.125
TET	≤1	≥64	2

^aStrain EC38 had two major bands with pIs of 5.4 and >9, and strain EC44 had one major band with a pI of >9.

^bAMP, ampicillin; ATM, aztreonam; CTR, ceftriaxone; CAZ, ceftazidime; CTX, cefotaxime; FOX, cefoxitin; AMX, amoxicillin; CFZ, cefazolin; CFX, cefixime; AMK, amikacin; IPM, imipenem; CIP, ciprofloxacin; TET, tetracycline; CLA, clavulanic acid at a fixed concentration 4 μg/ml when tested with ceftazidime, cefotaxime, and ceftriaxone and at a ratio of 2:1 when tested with amoxicillin.