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. 2009 Mar 30;53(6):2483–2491. doi: 10.1128/AAC.00428-08

TABLE 3.

Cross-resistance, increased β-lactamase activity, and expression of efflux pumps in resistant coloniesa

Antibiotic used for selectionb and strain MIC (μg/ml)c
Fold changed in:
β-Lactamase activitye
Efflux pump expression
CAZ CIP TOB CHL TET Basal Induced mexF mexD mexB mexY
None, PAO1 2 0.19 1.5 32 4
CAZ
    PAO1 20 0.125 1.75 ND ND 4.4 1.07 ND ND ND ND
    mutT mutant 18 0.17 2 ND ND 5.6 0.78 ND ND ND ND
    mutY mutant 26 0.13 2 ND ND 4.9 0.88 ND ND ND ND
    mutM mutant 18 0.16 2 ND ND 5.4 0.87 ND ND ND ND
TOB
    PAO1 0.5 0.32 6 28 (+) 10 ND ND 1.18 1.88 1.29 2.4
    mutT mutant 0.69 0.16 3.75 86 (+) 5.5 ND ND 1.04 0.86 0.89 0.76
    mutY mutant 0.63 0.11 3.5 56 (+) 18 ND ND 2.05 1.57 0.94 2
    mutM mutant 0.38 0.08 0.9 20 (+) 4.25 ND ND ND ND ND ND
CIP
    PAO1 0.44 0.75 1.06 >256 >256 ND ND 1.25 618.73 5.5 1.77
    mutT mutant 0.47 0.75 1.37 >256 >256 ND ND 0.97 607.77 1.07 1.04
    mutY mutant 0.44 0.88 1.19 >256 >256 ND ND 0.75 437.72 0.59 0.89
    mutM mutant 0.44 0.75 1.25 >256 >256 ND ND 11.3 342.16 0.73 5.7
a

From the population analysis of the GO gene (mutT, mutY, and mutM) mutants isolated after selection on ceftazidime, tobramycin, or ciprofloxacin.

b

CAZ, ceftazidime; TOB, tobramycin; CIP, ciprofloxacin.

c

Each MIC is the mean for four colonies (two successive determinations per colony), except for PAO1 after selection on tobramycin, where the MIC is the mean for two colonies. CHL, chloramphenicol; TET, tetracycline; ND, not detected. Plus signs in parentheses indicate that the colonies isolated from LB agar plates containing tobramycin showed a small subpopulation resistant to chloramphenicol.

d

Relative to the respective nonresistant strain.

e

The induced β-lactamase activity of PAO1 was 26.5-fold higher than its basal β-lactamase activity.