Table 2.
Fractional inhibitory concentration (FIC) and FIC indices (FICI) of octenidine dihydrochloride (OCT)—lavender essential oil (LEO) pairs against methicillin-resistant Staphylococcus aureus (MRSA) strains.
| Bacteria | OCT-LEO | MICo | MBC | MICc | FIC | FICI | Type of Interaction | |
|---|---|---|---|---|---|---|---|---|
| reference strain | ATCC 43300 | OCT (µg/mL) | 1.95 ± 0.00 | 5.21 ± 2.26 | 0.12 ± 0.00 | 0.06 | 0.11 | synergy |
| LEO (mg/mL) | 18.29 ± 7.92 | 439.00 ± 0.00 | 0.86 ± 0.00 | 0.05 | ||||
| isolates | 1 | OCT (µg/mL) | 3.91 ± 0.00 | 11.72 ± 5.52 | 0.12 ± 0.00 | 0.03 | 0.16 | synergy |
| LEO (mg/mL) | 13.72 ± 0.00 | 27.44 ± 0.00 | 1.71 ± 0.00 | 0.13 | ||||
| 2 | OCT (µg/mL) | 3.52 ± 0.00 | 7.04 ± 0.00 | 0.24 ± 0.00 | 0.13 | 0.26 | synergy | |
| LEO (mg/mL) | 13.72 ± 0.00 | 27.44 ± 0.00 | 1.71 ± 0.00 | 0.13 | ||||
| 3 | OCT (µg/mL) | 3.52 ± 0.00 | 7.04 ± 0.00 | 0.12 ± 0.00 | 0.06 | 0.12 | synergy | |
| LEO (mg/mL) | 13.72 ± 0.00 | 27.44 ± 0.00 | 0.86 ± 0.00 | 0.06 |
Values are expressed as mean ± standard deviation. MICo, minimum inhibitory concentration of OCT or LEO; MBC, minimum bactericidal concentration; MICc, minimum inhibitory concentration of OCT/LEO combination. FIC index = FIC of OCT + FIC of LEO. FICI < 0.5, synergy; 0.5 ≤ FICI ≤ 1.0, addition; 1.1 < FICI ≤ 4.0, indifference; FICI > 4.0, antagonism. Using the known density of LEO, the final result was expressed in mg/mL.