Table 2.
Fractional inhibitory concentration (FIC) and FIC indices (FICIs) of pairs of essential oil compounds (EOCs) and β-lactam antibiotics (βLAs) against Staphylococcus aureus ATCC 43300 strain.
| EOC–βLA | MICo | MICc | FIC | FICI | Type of Interaction |
|---|---|---|---|---|---|
| Methicillin–1,8-Cineole | |||||
| Methicillin (mg/L) | 7.8 ± 0.0 | 7.8 ± 0.0 | 1.0 | 2.0 | Indifference |
| 1,8-Cineole (mg/mL) | 115.1 ± 0.0 | 115.1 ± 0.0 | 1.0 | ||
| Methicillin–Eugenol | |||||
| Methicillin (mg/L) | 7.8 ± 0.0 | 7.8 ± 0.0 | 1.0 | 2.5 | Indifference |
| Eugenol (mg/mL) | 11.1 ± 4.8 | 16.7 ± 0.0 | 1.5 | ||
| Methicillin–Carvacrol | |||||
| Methicillin (mg/L) | 7.8 ± 0.0 | 7.8 ± 0.0 | 1.0 | 3.4 | Indifference |
| Carvacrol (mg/mL) | 3.2 ± 1.1 | 7.6 ± 0.0 | 2.4 | ||
| Methicillin–Linalool | |||||
| Methicillin (mg/L) | 7.8 ± 0.0 | 7.8 ± 0.0 | 1.0 | 2.0 | Indifference |
| Linalool (mg/mL) | 6.8 ± 0.0 | 6.8 ± 0.0 | 1.0 | ||
| Methicillin–Linalyl acetate | |||||
| Methicillin (mg/L) | 7.8 ± 0.0 | 2.0 ± 0.0 | 0.3 | 0.4 | Synergy |
| Linalyl acetate (mg/mL) | 46.9 ± 16.3 | 7.0 ± 0.0 | 0.1 | ||
| Methicillin–trans-Anethole | |||||
| Methicillin (mg/L) | 7.8 ± 0.0 | 7.8 ± 0.0 | 1.0 | 2.0 | Indifference |
| trans-Anethole (mg/mL) | 494.0 ± 0.0 | 494.0 ± 0.0 | 1.0 | ||
| Methicillin–Thymol | |||||
| Methicillin (mg/L) | 7.8 ± 0.0 | 15.6 ± 0.0 | 2.0 | 5.0 | Antagonism |
| Thymol (mg/mL) | 0.8 ± 0.4 | 2.5 ± 0.0 | 3.0 | ||
| Methicillin–Menthone | |||||
| Methicillin (mg/L) | 7.8 ± 0.0 | 31.3 ± 0.0 | 4.0 | 6.0 | Antagonism |
| Menthone (mg/mL) | 27.9 ± 0.0 | 55.8 ± 0.0 | 2.0 | ||
| Penicillin G–1,8-Cineole | |||||
| Penicillin G (mg/L) | 3.9 ± 0.0 | 0.2 ± 0.0 | 0.05 | 0.1 | Synergy |
| 1,8-Cineole (mg/mL) | 115.1 ± 0.0 | 3.6 ± 0.0 | 0.03 | ||
| Penicillin G–Eugenol | |||||
| Penicillin G (mg/L) | 3.9 ± 0.0 | 2.0 ± 0.0 | 0.5 | 1.2 | Indifference |
| Eugenol (mg/mL) | 11.1 ± 4.8 | 8.3 ± 0.0 | 0.7 | ||
| Penicillin G–Carvacrol | |||||
| Penicillin G (mg/L) | 3.9 ± 0.0 | 2.0 ± 0.0 | 0.5 | 1.7 | Indifference |
| Carvacrol (mg/mL) | 3.2 ± 1.1 | 3.8 ± 0.0 | 1.2 | ||
| Penicillin G–Linalool | |||||
| Penicillin G (mg/L) | 3.9 ± 0.0 | 2.0 ± 0.0 | 0.5 | 1.5 | Indifference |
| Linalool (mg/mL) | 6.8 ± 0.0 | 6.8 ± 0.0 | 1.0 | ||
| Penicillin G–Linalyl acetate | |||||
| Penicillin G (mg/L) | 3.9 ± 0.0 | 2.0 ± 0.0 | 0.5 | 0.6 | Addition |
| Linalyl acetate (mg/mL) | 46.9 ± 16.3 | 3.5 ± 0.0 | 0.1 | ||
| Penicillin G–trans-Anethole | |||||
| Penicillin G (mg/L) | 3.9 ± 0.0 | 3.9 ± 0.0 | 1.0 | 1.5 | Indifference |
| trans-Anethole (mg/mL) | 494.0 ± 0.0 | 247.0 ± 0.0 | 0.5 | ||
| Penicillin G–Thymol | |||||
| Penicillin G (mg/L) | 3.9 ± 0.0 | 2.0 ± 0.0 | 0.5 | 1.3 | Indifference |
| Thymol (mg/mL) | 0.8 ± 0.4 | 0.6 ± 0.0 | 0.8 | ||
| Penicillin G–Menthone | |||||
| Penicillin G (mg/L) | 3.9 ± 0.0 | 2.0 ± 0.0 | 0.5 | 1.5 | Indifference |
| Menthone (mg/mL) | 27.9 ± 0.0 | 27.9 ± 0.0 | 1.0 | ||
MICo, minimal inhibitory concentration of EOC or βLA; MICc, minimal inhibitory concentration of EOC/βLA combination. FIC index = FIC of EOC + FIC of βLA. FICI < 0.5, synergy; 0.5 ≤ FICI ≤ 1.0, addition; 1.1 < FICI ≤ 4.0, indifference; FICI > 4.0, antagonism. Values are expressed as mean ± standard deviation.