Table 3. In vitro interaction effects between AMPs (S61, S62, S63) and clarithromycin against M. abscessus clinical isolates.
| Isolates | Type of CLA resistance | MIC of CLA (μg/ml) | MIC (μg/ml) | FICIa | MIC (μg/ml) | FICIa | MIC (μg/ml) | FICIa | |||
|---|---|---|---|---|---|---|---|---|---|---|---|
| S61 alone | Combined CLA (μg/ml) + S61 (μM) | S62 alone | Combined CLA (μg/ml) + S62 (μM) | S63 alone | Combined CLA (μg/ml) + S63 (μM) | ||||||
| MAB01 | Acquired | 1,024 | 6.25 | 32/2.34 | 0.41±0.17 (Syn) | 12.5 | 96/2.34 | 0.28±0.13 (Syn) | 6.25 | 256/2.34 | 0.63±0.17 (Add) |
| MAB02 | Inducible | 64 | >400 | 64/6.25 | 1.02±0.00 (Ind) | >400 | 64/3.13 | 1.01±0.00 (Ind) | >400 | 64/14.06 | 1.04±0.04 (Ind) |
| MAB03 | Acquired | 8 | 6.25 | 2/0.20 | 0.28±0.00 (Syn) | 25 | 1.5/2.34 | 0.38±0.17 (Syn) | 12.5 | 4/0.20 | 0.52±0.00 (Add) |
| MAB05 | Inducible | 16 | >400 | 16/3.13 | 1.01±0.00 (Ind) | >400 | 16/3.13 | 1.01±0.00 (Ind) | >400 | 16/3.13 | 1.01±0.00 (Ind) |
| MAB07 | Inducible | 16 | >400 | 0.25/6.25 | 0.03±0.00 (Syn) | >400 | 0.25/3.13 | 0.02±0.00 (Syn) | >400 | 0.25/9.38 | 0.04±0.01 (Syn) |
| MAB09 | Inducible | 8 | >400 | 8/3.13 | 1.01±0.00 (Ind) | >400 | 6/3.13 | 0.76±0.35 (Add) | >400 | 4/6.25 | 0.52±0.00 (Add) |
| MAB10 | Acquired | 1,024 | >400 | 32/6.25 | 0.05±0.00 (Syn) | >400 | 32/18.75 | 0.08±0.02 (Syn) | >400 | 8/25 | 0.07±0.00 (Syn) |
| MAB11 | Inducible | 512 | >400 | 128/75 | 0.67±0.08 (Add) | >400 | 192/3.13 | 0.76±0.35 (Add) | >400 | 192/3.13 | 0.76±0.35 (Add) |
| MAB12 | Acquired | 1,024 | >400 | 1,024/3.13 | 1.01±0.00 (Ind) | >400 | 1,024/3.13 | 1.01±0.00 (Ind) | >400 | 1,024/3.13 | 1.01±0.00 (Ind) |
| MAB14 | Acquired | 512 | >400 | 4/37.5 | 0.10±0.04 (Syn) | >400 | 4/75 | 0.20±0.09 (Syn) | >400 | 32/50 | 0.19±0.00 (Syn) |
Note: AMP, antimicrobial peptide; MIC, minimal inhibitory concentration; CLA, clarithromycin; FICI, fractional inhibitory concentration index.
Ten clinical isolate representatives from the phylogenetic tree covering inducible and acquired resistances of two Mab subsp. that were selected for the AMP-clarithromycin interaction assay. The data exhibited mean ± S.D. of FICI values that were measured in two independent experiments.
aFICI interpretation: < 0.5: synergy (Syn); 0.5–1.0: additive (Add); > 1–4.0: indifference (Ind); > 4.0: antagonism (Ant).
Gray-shaded boxes show synergistic interaction.