TABLE 2.

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

Antimicrobial drugMIC (μg/ml) (fold increase)a
E. coli DH10BE. coli DH10B(pBR322)E. coli DH10B+pBR322) qnrA1E. coli DH10B(pBR322) qnrS1E. coli DH10B(pBR322) qnrDE. coli DH10B(p2007057)
Ciprofloxacin0.0020.0040.125 (64)0.5 (256)0.06 (32)0.125 (64)
Norfloxacin0.0150.0150.25 (16)0.5 (32)0.06 (4)0.125 (64)
Ofloxacin0.0150.0320.25 (16)0.5 (32)0.125 (8)0.25 (16)
Nalidixic acid228 (4)8 (4)4 (2)8 (4)
  • a All MIC determinations were performed in broth microdilution assays according to CLSI standards (8).