TABLE 2.

Results of susceptibility testing by broth microdilution of Escherichia coli DH10B and isogenic strains carrying qnr genes

Antimicrobial drug	MIC (μg/ml) (fold increase)a
	E. coli DH10B	E. coli DH10B(pBR322)	E. coli DH10B+pBR322) qnrA1	E. coli DH10B(pBR322) qnrS1	E. coli DH10B(pBR322) qnrD	E. coli DH10B(p2007057)
Ciprofloxacin	0.002	0.004	0.125 (64)	0.5 (256)	0.06 (32)	0.125 (64)
Norfloxacin	0.015	0.015	0.25 (16)	0.5 (32)	0.06 (4)	0.125 (64)
Ofloxacin	0.015	0.032	0.25 (16)	0.5 (32)	0.125 (8)	0.25 (16)
Nalidixic acid	2	2	8 (4)	8 (4)	4 (2)	8 (4)

^aAll MIC determinations were performed in broth microdilution assays according to CLSI standards (8).