Table 2

Determination of antibiotic MICs for WT, ΔkpnEF, and ΔkpnEFΩkpnEF strainsa

AntibioticMIC (μg/ml) for the WT strainMIC (μg/ml) for the ΔkpnEF strainFold change (WT/ΔkpnEF strain)MIC (μg/ml) for the ΔkpnEFΩkpnEF strain
Cefepime2.0481.02422.048
Ceftazidime0.2560.06440.256
Chloramphenicol0.10.110.1
Ciprofloxacin<0.01<0.0052<0.01
Colistin0.010.00520.01
Erythromycin>422>4
Kanamycin1>30301
Norfloxacin<0.001<0.0011<0.001
Polymyxin0.10.0520.1
Rifampin105210
Sparfloxacin<0.01<0.011<0.01
Streptomycin0.10.01100.1
Tetracycline52.525
Tobramycin0.10.110.1
Vancomycin>4>41>4
  • a E-strips were used to determine the precise MICs for different antibiotics, such as amikacin, ampicillin, cefepime, cefotaxime, ceftazidime, ceftriaxone, chloramphenicol, ciprofloxacin, colistin, erythromycin, kanamycin, nalidixic acid, norfloxacin, ofloxacin, polymyxin, rifampin, sparfloxacin, streptomycin, tetracycline, tobramycin, trimethoprim, and vancomycin, according to the CLSI guidelines (31). Representative antibiotics are shown here. The resistance to kanamycin in the ΔkpnEF strain is due to the insertion of a plasmid that carries the Kanr gene. The fold change indicates the ratio of MICs for the WT and ΔkpnEF strains.