TABLE 1.

Conditions and concentrations of antibiotics used in this study

Exposure group and E. coli strain	Antibiotic(s)a	Concn range (μg/ml)d
Ampicillin and/or tetracycline (administered separately or in combination)
MG1655	Ampicillin, tetracycline	0.0000005-500
	Mixture of ampicillin and tetracyclineb	0.0000005-500
MG1655(pBR322)	Ampicillin, tetracycline	0.0000005-500
	Mixture of ampicillin and tetracyclineb	0.0000005-500
Ampicillin (administered separately or in combination with tetracycline)
OCL62	Ampicillin	0.0005-50
OCL62(pBR322)	Ampicillin	0.0005-50
	Mixture of ampicillin and tetracyclineb	0.0005-50
Penicillin, erythromycin, chloramphenicol, kanamycin, and/or gentamicin (administered separately or in combination with the mixture of ampicillin and tetracycline [5 μg/ml each])
MG1655(pBR322)	Penicillin, erythromycin, chloramphenicol, kanamycin, and gentamicin	0.0005-50
	Mixture of ampicillin and tetracyclinec + penicillin	0.000005-50
	Mixture of ampicillin and tetracyclinec + erythromycin	0.000005-50
	Mixture of ampicillin and tetracyclinec + chloramphenicol	0.000005-50
	Mixture of ampicillin and tetracyclinec + kanamycin	0.000005-50
	Mixture of ampicillin and tetracyclinec + gentamicin	0.000005-50
Ni2+, Na+, and Mg2+ salts (administered separately or in combination with the mixture of ampicillin and tetracycline [5 μg/ml each])
MG1655(pBR322)	Mixture of ampicillin and tetracyclinec + NiCl2	0.001-1000
	Mixture of ampicillin and tetracyclinec + NaCl	0.005-5000
	Mixture of ampicillin and tetracyclinec + MgCl2	0.001-1000

^aThe antibiotic(s) was administered separately or in combination, depending on each condition.

^bThe mixture of ampicillin and tetracycline was diluted to concentrations of 0.0000005 to 500 μg/ml each.

^cThe mixture of ampicillin and tetracycline was fixed at concentrations of 5 μg/ml each.

^dWith a series of 10-fold dilutions.