Table 1. MICs of colistin, sulbactam, and fosfomycin as monotherapy and combination regimens and the FICI-against carbapenem-resistant Acinetobacter baumannii isolates (n = 50).
| Isolate | MIC (µg/mL) | Synergy study | |||||||
|---|---|---|---|---|---|---|---|---|---|
| CST | SUL | FOF | CST (+ SUL) | CST (+ FOF) | FICI (CST + SUL) | Result | FICI (CST + FOF) | Result | |
| 1 | 1 | 32 | 2,048 | 1 | 0.25 | 1.06 | IND | 0.5 | SYN |
| 2 | 1 | 64 | 128 | 0.5 | 0.5 | 0.52 | ADD | 1.5 | IND |
| 3 | 1 | 64 | 256 | 0.25 | 0.5 | 0.75 | ADD | 1 | ADD |
| 4 | 1 | 64 | 256 | 0.25 | 0.5 | 0.5 | SYN | 1 | ADD |
| 5 | 1 | 64 | 128 | 0.25 | 0.5 | 0.5 | SYN | 1.5 | IND |
| 6 | 1 | 128 | 2,048 | 0.0625 | 0.5 | 0.56 | ADD | 0.63 | ADD |
| 7 | 1 | 256 | 2,048 | 0.5 | 0.5 | 0.53 | ADD | 0.56 | ADD |
| 8 | 1 | 64 | 128 | 0.25 | 0.5 | 0.5 | SYN | 1.5 | IND |
| 9 | 1 | 128 | 1,024 | 0.5 | 0.25 | 0.63 | ADD | 0.3125 | SYN |
| 10 | 1 | 16 | 128 | 1 | 0.5 | 1.13 | IND | 1.5 | IND |
| 11 | 1 | 64 | 256 | 0.5 | 0.5 | 0.75 | ADD | 0.75 | ADD |
| 12 | 2 | 64 | 512 | 0.5 | 0.5 | 0.5 | SYN | 0.75 | ADD |
| 13 | 16 | 64 | 512 | 0.25 | 0.5 | 0.52 | ADD | 0.28 | SYN |
| 14 | 1 | 32 | 512 | 0.5 | 0.5 | 1 | ADD | 0.75 | ADD |
| 15 | 1 | 64 | 256 | 0.5 | 0.5 | 1 | ADD | 1 | ADD |
| 16 | 1 | 64 | 256 | 0.5 | 0.25 | 1 | ADD | 0.75 | ADD |
| 17 | 1 | 32 | 256 | 0.0625 | 0.25 | 0.31 | SYN | 0.75 | ADD |
| 18 | 1 | 32 | 2,048 | 0.5 | 0.0625 | 1 | ADD | 0.56 | ADD |
| 19 | 1 | 64 | 2,048 | 0.25 | 0.0625 | 0.5 | SYN | 0.56 | ADD |
| 20 | 1 | 64 | 512 | 0.5 | 0.25 | 1 | ADD | 0.75 | ADD |
| 21 | 16 | 64 | 256 | 0.5 | 0.25 | 0.16 | SYN | 1.02 | IND |
| 22 | 1 | 128 | 256 | 0.5 | 0.25 | 0.75 | ADD | 0.75 | ADD |
| 23 | 1 | 64 | 256 | 0.5 | 0.5 | 1 | ADD | 1 | ADD |
| 24 | 16 | 64 | 512 | 0.25 | 0.25 | 0.27 | SYN | 0.27 | SYN |
| 25 | 16 | 32 | 256 | 1 | 2 | 1.06 | IND | 0.63 | ADD |
| 26 | 16 | 32 | 256 | 0.25 | 1 | 1.02 | IND | 0.56 | ADD |
| 27 | 1 | 128 | 256 | 0.5 | 0.5 | 0.63 | ADD | 1 | ADD |
| 28 | 1 | 16 | 256 | 0.5 | 0.5 | 1 | ADD | 0.75 | ADD |
| 29 | 1 | 64 | 256 | 0.5 | 0.5 | 0.63 | ADD | 1 | ADD |
| 30 | 2 | 128 | 256 | 0.5 | 0.5 | 0.5 | SYN | 0.5 | SYN |
| 31 | 1 | 128 | 256 | 0.5 | 0.5 | 0.75 | ADD | 1 | ADD |
| 32 | 1 | 64 | 128 | 0.5 | 0.5 | 1 | ADD | 1 | ADD |
| 33 | 1 | 32 | 256 | 0.5 | 0.5 | 1 | ADD | 0.75 | ADD |
| 34 | 1 | 128 | 256 | 0.5 | 0.25 | 0.63 | ADD | 0.5 | SYN |
| 35 | 1 | 64 | 256 | 0.5 | 0.125 | 0.56 | ADD | 0.63 | ADD |
| 36 | 1 | 64 | 256 | 0.5 | 0.25 | 1 | ADD | 0.75 | ADD |
| 37 | 1 | 64 | 128 | 0.125 | 0.5 | 1.13 | IND | 1 | ADD |
| 38 | 1 | 64 | 1,024 | 0.5 | 0.5 | 0.75 | ADD | 0.63 | ADD |
| 39 | 1 | 128 | 512 | 0.5 | 0.25 | 0.56 | ADD | 0.5 | SYN |
| 40 | 1 | 128 | 256 | 0.5 | 0.25 | 0.63 | ADD | 0.75 | ADD |
| 41 | 1 | 32 | 256 | 0.5 | 0.25 | 1.5 | IND | 0.75 | ADD |
| 42 | 2 | 2,048 | 256 | 0.125 | 0.25 | 0.07 | SYN | 0.63 | ADD |
| 43 | 2 | 256 | 1,024 | 0.5 | 0.25 | 0.38 | SYN | 0.25 | SYN |
| 44 | 2 | 256 | 2,048 | 0.25 | 0.5 | 0.38 | SYN | 0.38 | SYN |
| 45 | 1 | 64 | 256 | 0.0625 | 0.5 | 1.06 | IND | 1 | ADD |
| 46 | 2 | 2,048 | 1,024 | 0.5 | 0.5 | 0.26 | SYN | 0.38 | SYN |
| 47 | 1 | 64 | 512 | 0.25 | 0.5 | 0.5 | SYN | 0.75 | ADD |
| 48 | 1 | 16 | 256 | 0.5 | 1 | 1 | ADD | 1.25 | IND |
| 49 | 2 | 64 | 512 | 0.5 | 0.5 | 0.5 | SYN | 0.5 | SYN |
| 50 | 1 | 64 | 256 | 0.5 | 0.5 | 1 | ADD | 1 | ADD |
| MIC50 | 1 | 64 | 256 | 0.5 | 0.5 | SYN | 15 (30%) | SYN | 11 (22%) |
| MIC90 | 4 | 128 | 2,048 | 0.5 | 0.5 | ADD | 28 (56%) | ADD | 33 (66%) |
| Min | 1 | 16 | 128 | 0.0625 | 0.0625 | IND | 7 (14%) | IND | 6 (12%) |
| Max | 16 | 2,048 | 2,048 | 1 | 2 | Total | 50 | Total | 50 |
MIC, minimum inhibitory concentration; FICI, fractional inhibitory concentration index; CST, colistin; SUL, sulbactam; FOF, fosfomycin; IND, indifference (FICI = 1 - 4); SYN, synergistic effect (FICI ≤0.5); ADD, additive effect (FICI 0.5 - ≤1); Max, maximum; Min, minimum; MIC50, 50% minimum inhibitory concentration; MIC90, 90% minimum inhibitory concentration.