Table 2.
Activity of lavender essential oils from leafy stalks in combination with gentamicin against selected bacterial strains.
| Antibacterial Agent | Blue River | Ellagance Purple | Type of Interaction | ||||||
|---|---|---|---|---|---|---|---|---|---|
| MIC0 | MICc | FIC | FICI | MIC0 | MICc | FIC | FICI | ||
| Staphylococcus aureus ATCC 25923 | |||||||||
| Essential oil (% v/v) | 0.500 | 0.032 | 0.164 | 0.192 | 0.250 | 0.016 | 0.064 | 0.320 | synergistic |
| Gentamicin (µg/mL) | 0.125 | 0.016 | 0.128 | 0.125 | 0.032 | 0.256 | |||
| Staphylococcus aureus MRSA | |||||||||
| Essential oil (% v/v) | 1.250 | 0.016 | 0.013 | 0.076 | 1.250 | 0.032 | 0.026 | 0.089 | synergistic |
| Gentamicin (µg/mL) | 32.0 | 2.0 | 0.063 | 32.0 | 2.0 | 0.063 | |||
| Pseudomonas aeruginosa ATCC 9027 | |||||||||
| Essential oil (% v/v) | 1.50 | 1.0 | 0.666 | 1.166 | 2.5 | 2.0 | 0.80 | 1.300 | no interaction |
| Gentamicin (µg/mL) | 2.0 | 1.0 | 0.500 | 2.0 | 1.0 | 0.50 | |||
Explanations: MIC—minimal inhibitory concentration; FIC—fractional inhibitory concentration; FICI—fractional inhibitory concentration index; MIC0 = MIC of an individual sample alone; MICc = MIC of an individual sample of the most effective combination; FIC of essential oil = MIC of essential oil in combination with gentamicin/MIC of essential oil alone; FIC of gentamicin = MIC of gentamicin in combination with essential oil/MIC of gentamicin alone; FICI = FIC of essential oil + FIC of gentamicin. Interpretation: FICI ≤ 0.5, synergistic; FICI > 0.5–1.0, additive; FICI > 1.0–4.0, no interaction; FICI > 4.0, antagonistic [30].