TABLE 2.
Phenotypic and genotypic characterization of parent and mutant strains selected during treatment with meropenem and ceftazidimea
| Antimicrobial agent | P. aeruginosa strain | MIC (mg/liter) of:
|
Efflux pump inhibition test
|
Cephalosporinase inhibition test
|
Modification(s) in:
|
|||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Inhibition zone diam (mm) for CAZ (30 μg)
|
Difference in inhibition zone diam (mm) | Result | ||||||||||||||
| MEM | IMP | CAZ | PIP | PIP-TAZ | MIC (mg/liter) of LEV
|
Reduction of MIC (n-fold) | Result | Without cloxacillin | With cloxacillinc | OprD | AmpD | |||||
| Without Phe-Arg-β-naphthylamide | With Phe-Arg-β-naphthylamideb | |||||||||||||||
| MEM | PAO1 | 0.5 | 2 | 0.5 | 0.06 | 8 | − | None | ||||||||
| 12-09-15 | 2 | 4 | 128 | 2 | 64 | + | None | |||||||||
| PAO1/MEM | 4 | 16 | 0.5 | 0.12 | 4 | − | Insertion of C after A1205; frameshift | |||||||||
| 12-09-15/MEM | 16 | 16 | 64 | 1 | 64 | + | None | |||||||||
| CAZ | PAO1 | 2 | 4 | 4 | 0.5 | 0.06 | 8 | − | 27 | 27 | 0 | − | None | |||
| PAO1/CAZ | 32 | 64 | 64 | 0.5 | 0.06 | 8 | − | 17 | 27 | 10 | + | None | ||||
a
MEM, meropenem; IMP, imipenem; CAZ, ceftazidime; PIP, piperacillin; PIP-TAZ, piperacillin-tazobactam; LEV, levofloxacin; +, overproduction of efflux pumps or AmpC β-lactamase; −, no overproduction of efflux pumps or AmpC β-lactamase.
b
Phe-Arg-β-naphthylamide was included at 20 mg/liter.
c
Cloxacillin was included at 500 mg/liter.