Table 2.
Antimicrobial combination test against carbapenem-resistant A. baumannii clinical isolates using chequerboard technique.
| Strains | REP-PCR group | Colistin + sulbactam | Colistin + fosfomycin | ||||||
|---|---|---|---|---|---|---|---|---|---|
| FICI (Col) |
FICI (Sul) |
ΣFICI (Col + Sul) | Interpretation (Col + Sul) |
FICI (Col) |
FICI (Fos) |
ΣFICI (Col + Fos) |
Interpretation (Col + Fos) |
||
| AB 1 | A | 0.06 | 2 | 2.06 | Indifference | 0.5 | 0.5 | 1 | Additive |
| AB 2 | A | 0.25 | 0.5 | 0.75 | Additive | 0.5 | 0.13 | 0.63 | Additive |
| AB 4 | A | 0.13 | 0.25 | 0.38 | Synergism | 0.5 | 0.25 | 0.75 | Additive |
| AB 6 | A | 0.5 | 0.06 | 0.56 | Additive | 0.5 | 0.25 | 0.75 | Additive |
| AB 7 | A | 0.25 | 0.25 | 0.5 | Synergism | 0.25 | 0.13 | 0.38 | Synergism |
| AB 13 | A | 0.13 | 0.5 | 0.63 | Additive | 0.13 | 1 | 1.13 | Indifference |
| AB 14 | A | 0.5 | 0.5 | 1 | Additive | 0.5 | 0.5 | 1 | Additive |
| AB 15 | A | 0.03 | 1 | 1.03 | Indifference | 0.13 | 0.25 | 0.38 | Synergism |
| AB 3 | B | 0.5 | 0.5 | 1 | Additive | 1 | 0.25 | 1.25 | Indifference |
| AB 5 | C | 0.13 | 1.0 | 1.13 | Indifference | 0.25 | 0.25 | 0.5 | Synergism |
| AB 8 | D | 0.06 | 1 | 1.06 | Indifference | 0.25 | 0.5 | 0.75 | Additive |
| AB 9 | E | 0.008 | 1 | 1.01 | Indifference | 0.03 | 0.25 | 0.28 | Synergism |
| AB 10 | F | 0.004 | 2 | 2.00 | Indifference | 0.02 | 1 | 1.02 | Indifference |
| AB 11 | G | 1 | 0.004 | 1.004 | Indifference | 0.01 | 1 | 1.01 | Indifference |
| AB 12 | H | 0.06 | 0.5 | 0.56 | Additive | 0.25 | 0.5 | 0.75 | Additive |
The fractional inhibitory concentration indices (FICI) were interpreted as ≤0.5 = synergistic, >0.5–<1.0 = additive effect, >1–4 = indifference, and ≥4 antagonistic effect.