Table 2.
The fractional inhibitory concentration (FIC) and FIC index (FICI) for the carvacrol and antibiotic combinations against Streptococcus pyogenes.
| Combinations | ATCC 19615 | Clinical isolate | |||||||
|---|---|---|---|---|---|---|---|---|---|
| A | B | FIC A | FIC B | ΣFICI | Interpretation | FIC A | FIC B | ΣFICI | Interpretation |
| Carvacrol | Penicillin G | 0.5 | 1 | 1.5 | IND | 0.5 | 1 | 1.5 | IND |
| Carvacrol | Penicillin Vk | 0.5 | 1 | 1.5 | IND | 0.5 | 0.5 | 1 | ADD |
| Carvacrol | Clindamycin | 0.5 | 0.5 | 1 | ADD | 0 | 1 | 1 | ADD |
| Carvacrol | Erythromycin | 0.25 | 1 | 1.25 | IND | – | – | – | – |
Fractional inhibitory concentrations (FICs) and fractional inhibitory concentration index (FICIs) were calculated FICI = ΣFIC = FICA + FICB where, MICA value is the MIC of compound A alone, MICB value is the MIC of compound B alone, and MICA+B value is the MIC of compound A in the presence of compound B, and vice versa for MICB+A.
FICIs were interpreted as SYN, synergy (FICI ≤ 0.5); ADD, additive synergy (> 0.5 FICI ≤ 1.0); IND, indifference/no interaction (> 1.0 FICI ≥ 4.0); and ANT, antagonism (FICI Index > 4.0).