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 |
From the population analysis of the GO gene (mutT, mutY, and mutM) mutants isolated after selection on ceftazidime, tobramycin, or ciprofloxacin.
CAZ, ceftazidime; TOB, tobramycin; CIP, ciprofloxacin.
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.
Relative to the respective nonresistant strain.
The induced β-lactamase activity of PAO1 was 26.5-fold higher than its basal β-lactamase activity.