TABLE 1.
Effect of PEI on efficacies of different families of antibiotics against P. aeruginosa 100609
| Antibiotic class | Antibiotic | MIC (μg/ml) with:
|
Checkerboard FIC index (interpretationa) with PEI (250 μg/ml) | Checkerboard effect | Killing curve effect | |
|---|---|---|---|---|---|---|
| Antibiotic alone | Antibiotic and PEI (250 μg/ml) | |||||
| Novobiocin | Novobiocin | 1,600 | 140 | 70.10 (S) | Synergy | Synergy |
| Aminoglycosides | Tobramycin | 50 | 240 | 4.81 (I) | Antagonism | Indifference |
| Kanamycin A | 1,600 | 1,920 | 1.21 (I) | Indifference | NDb | |
| Gentamicin | 1,120 | 1,920 | 1.72 (I) | Indifference | ND | |
| Tetracyclines | Tetracycline | 20 | 20 | 1.00 (I) | Indifference | ND |
| Cephalosporins | Ceftazidime | 400 | 10 | 0.04 (S) | Synergy | Synergy |
| Cefotaxime | 960 | 120 | 0.14 (S) | Synergy | ND | |
| Chloramphenicol | Chloramphenicol | 100 | 40 | 0.41 (S) | Synergy | Synergy |
| Macrolides | Erythromycin | 140 | 140 | 1.00 (I) | Indifference | ND |
| Polymyxins | Polymyxin E | 5 | 10 | 2.01 (I) | Antagonism | ND |
| Polymyxin B | 5 | 10 | 2.01 (I) | Antagonism | Antagonism | |
| Rifamycins | Rifampin | 20 | 10 | 0.05 (S) | Synergy | Synergy |
| Cationic glycopeptides | Vancomycin | 1,120 | 3,800 | 3.40 (I) | Antagonism | Antagonism |
| Fluoroquinolones | Ciprofloxacin | 30 | 30 | 1.00 (I) | Indifference | Indifference |
| Ofloxacin | 10 | 10 | 1.00 (I) | Indifference | ND | |
| Norfloxacin | 15 | 10 | 0.68 (I) | Indifference | ND | |
| β-Lactams | Ampicillin | 2,240 | 100c | ND | ND | Synergy |
| Carbenicillin | 2,240 | 60c | ND | ND | Synergy | |
| Piperacillin | 40 | 7.5c | ND | ND | Synergy | |
| Ticarcillin | 1,120 | 20c | ND | ND | Synergy | |
a
S, synergy; I, indifference.
b
ND, not determined.
c
Synergy between β-lactams and PEI was investigated in a previous study in which the PEI concentration was 200 nM (11).