Table 5.
Correlation between FIC and the synergistic effect upon combination with antibacterial agents
| Bacterial strains ATCC | Antibiotics | MIC of B1 alone (μM) | MIC of B1 combined (μM) | MIC of antibiotic alone (μM) | MIC of antibiotic combined (μM) | (%) Reduction in antibiotic MIC | FIC index | Synergism |
|---|---|---|---|---|---|---|---|---|
| MR | LVX | 20 | 2.5 | 10 | 0.75 | 92.50% | 0.20 | Synergistic |
| S. aureus | CHL | 20 | 2.5 | 130 | 65 | 50.00% | 0.63 | Additive |
| 33591 | RIF | 20 | 2.5 | 0.04 | 0.00125 | 96.88% | 0.16 | Synergistic |
| AMP | 20 | 5 | 85 | 37.5 | 55.88% | 0.69 | Additive | |
| ERY | 20 | 2.5 | 125 | 3.5 | 97.20% | 0.15 | Synergistic | |
| MR | LVX | 20 | 5 | 10 | 4 | 60.00% | 0.65 | Additive |
| S. aureus | CHL | 20 | 2 | 15 | 4 | 73.33% | 0.37 | Synergistic |
| 43300 | RIF | 20 | 5 | 1 | 0.3 | 70.00% | 0.55 | Additive |
| AMP | 20 | 7.5 | 20 | 7.5 | 62.50% | 0.55 | Additive | |
| ERY | 20 | 2.5 | 100 | 20 | 80.00% | 0.75 | Additive | |
| MR | LVX | 20 | 7.5 | 10 | 7.5 | 25.00% | 0.33 | Synergistic |
| S. aureus | CHL | 20 | 0.25 | 25 | 5 | 80.00% | 1.13 | Indifferent |
| BAA-41 | RIF | 20 | 0.5 | 0.005 | 0.00075 | 85.00% | 0.21 | Synergistic |
| AMP | 20 | 3.75 | 40 | 15 | 62.50% | 0.18 | Synergistic | |
| ERY | 20 | 7.5 | 350 | 250 | 28.57% | 0.56 | Additive | |
| MDR | LVX | 10 | 2.5 | 12 | 5 | 58.33% | 1.09 | Indifferent |
| P. aeruginosa | CHL | 10 | 1.25 | 200 | 50 | 75.00% | 0.67 | Additive |
| BAA-2114 | RIF | 10 | 0.25 | 50 | 37.5 | 25.00% | 0.38 | Synergistic |
| AMP | 10 | 7.5 | >500 | 375 | – | – | – | |
| ERY | 10 | 2.5 | 125 | 37.5 | 70.00% | 0.55 | Additive |
Abbreviations: MR, methicillin resistant; MDR, Multidrug resistant; LVX, levofloxacin; CHL, chloramphenicol; RIF, rifampicin; AMP, ampicillin; ERY, erythromycin; MIC, minimum inhibitory concentration; FIC, fractional inhibitory concentration.