Table 3. Synergistic activity of five plant secondary metabolites combined with clarithromycin against 14 clarithromycin-resistant M. abscessus isolates.
| Isolates | Susceptibility profile |
Individual MIC (μg/mL) | Combination MIC (μg/mL) | FICI | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| CLA | RL008 | RL009 | RL011 | RL012 | RL013 | CLA/RL008 | CLA/RL009 | CLA/RL011 | CLA/RL012 | CLA/RL013 | RL008 | RL009 | RL011 | RL012 | RL013 | ||
| 81499 | Acquired | 64 | 128 | 128 | 64 | 128 | 128 | 4/16 | 32/128 | 64/128 | 4/8 | 16/64 | 0.19 | 1.50 | 2.00 | 0.13 | 0.75 |
| 82998 | Acquired | 16 | 128 | 128 | 128 | 128 | 128 | 8/32 | 2/32 | 8/64 | 8/128 | 8/32 | 0.75 | 0.38 | 1.00 | 1.50 | 0.75 |
| 83305 | Acquired | 16 | >128 | 128 | 128 | 128 | 128 | 16/128 | 2/128 | 16/128 | 4/128 | 4/64 | 2.00 | 1.13 | 2.00 | 1.25 | 0.75 |
| 83310 | Acquired | 4 | 128 | >128 | 128 | >128 | >128 | 1/8 | 2/8 | 1/8 | 4/8 | 1/8 | 0.31 | 0.56 | 0.31 | 1.06 | 0.31 |
| 81618 | Acquired | 64 | 128 | 16 | 32 | 128 | 128 | 64/128 | 32/64 | 64/128 | 64/128 | 64/128 | 2.00 | 1.00 | 2.00 | 2.00 | 2.00 |
| 80700 | Acquired | 512 | >128 | 128 | 64 | >128 | 128 | 512/128 | 512/128 | 512/128 | 512/128 | 512/128 | 2.00 | 2.00 | 2.00 | 2.00 | 2.00 |
| 81838 | Acquired | 16 | 128 | 128 | 128 | 128 | 128 | 1/8 | 1/8 | 1/8 | 1/8 | 1/8 | 0.13 | 0.13 | 0.13 | 0.13 | 0.13 |
| 82119 | Inducible | 512 | 128 | 16 | 64 | 64 | 128 | 32/8 | 512/128 | 512/64 | 64/128 | 512/64 | 0.50 | 2.00 | 1.50 | 1.13 | 1.5 |
| 80097 | Inducible | 512 | 128 | 16 | 64 | 64 | 128 | 32/8 | 64/32 | 32/64 | 64/32 | 128/64 | 0.13 | 0.38 | 0.56 | 0.38 | 0.75 |
| 80838 | Inducible | 128 | 128 | 128 | 128 | 128 | >128 | 32/8 | 32/16 | 64/8 | 16/16 | 16/32 | 0.31 | 0.38 | 0.56 | 0.25 | 0.38 |
| 80988 | Inducible | 4 | 128 | >128 | 64 | 128 | >128 | 2/8 | 1/32 | 1/8 | 2/8 | 2/8 | 0.56 | 0.50 | 0.31 | 0.56 | 0.56 |
| 80901 | Inducible | 16 | >128 | 128 | 128 | 128 | >128 | 4/8 | 4/8 | 4/8 | 4/8 | 4/16 | 0.31 | 0.31 | 0.31 | 0.31 | 0.38 |
| 82154 | Inducible | 32 | 128 | 32 | 64 | 64 | 128 | 4/16 | 8/16 | 8/16 | 8/32 | 8/16 | 0.25 | 0.38 | 0.38 | 0.50 | 0.38 |
| 81103 | Inducible | 64 | 128 | 128 | 64 | 128 | 128 | 32/8 | 16/32 | 16/128 | 8/32 | 16/32 | 0.56 | 0.50 | 1.25 | 0.38 | 0.50 |
| Numbers of isolates with synergistic activity (%) | 8 (57) | 8 (57) | 5 (35.7) | 7 (50) | 6 (42.9) | ||||||||||||
Notes:
MIC, minimum inhibitory concentration; CLA, clarithromycin; Acquired, acquired resistance; Inducible, inducible resistance; FICI, fractional inhibitory concentration index.
FICI interpretation: ≤0.5: synergy; >0.5–1.0: additive; >1.0–4.0: indifference; >4.0: antagonism (Doern, 2014).
Grey-shaded boxes shows synergistic effect.