Table 4.
The calculated FIC index values of the MEM + AK and MEM + TGC combinations against 28 XDR CR pathogens
| Isolate code | MIC of antimicrobial agents (µg/ml)/Susceptibility | MEM + AK | MEM + TGC | ||||
|---|---|---|---|---|---|---|---|
| MEM | AK | TGC | FIC index | Interpretation a | FIC index | Interpretation a | |
| AB-9G | 256/R | 1024/R | 2/S | 0.531 | Additive | 1.063 | Indifferent |
| AB-109A | 256/R | 1024/R | 0.5/S | 0.531 | Additive | 1 | Indifferent |
| AB-63 M | 1024/R | 64/R | 0.5/S | 0.516 | Additive | 1 | Additive |
| AB-30G | 512/R | 16/S | 2/S | 1 | Additive | 0.75 | Additive |
| AB-100 M | 1024/R | 512/R | 2/S | 0.75 | Additive | 0.75 | Additive |
| AB-55 M | 1024/R | 512/R | 1/S | 0.625 | Additive | 1 | Additive |
| AB-20G | 256/R | 64/R | 1/S | 1.5 | Indifferent | 0.75 | Additive |
| AB-3 M | 512/R | 512/R | 4/I | 0.625 | Additive | 0.531 | Additive |
| AB-14 M | 128/R | 256/R | 0.5/S | 1 | Additive | 1 | Additive |
| AB-37 M | 1024/R | 128/R | 2/S | 0.516 | Additive | 0.75 | Additive |
| AB-34 M | 128/R | 64/R | 1/S | 1 | Additive | 1 | Additive |
| AB-13 M | 512/R | 64/R | 2/S | 0.531 | Additive | 1.031 | Indifferent |
| AB-7G | 512/R | 64/R | 2/S | 0.531 | Additive | 0.75 | Additive |
| KP-84S | 64/R | 256/R | 4/I | 0.625 | Additive | 0.75 | Additive |
| KP-25S | 1024/R | 1024/R | 4/I | 0.75 | Additive | 0.531 | Additive |
| KP-89S | 128/R | 256/R | 4/I | 1 | Additive | 0.75 | Additive |
| KP-106S | 512/R | 512/R | 2/S | 0.625 | Additive | 1.031 | Indifferent |
| KP-114S | 1024/R | 16/S | 0.5/S | 0.625 | Additive | 1 | Additive |
| KP-92A | 1024/R | 64/R | 4/I | 0.516 | Additive | 0.531 | Additive |
| KP-79A | 512/R | 64/R | 4/I | 0.531 | Additive | 0.531 | Additive |
| KP-113S | 512/R | 512/R | 1/S | 0.625 | Additive | 1.063 | Indifferent |
| PA-78S | 128/R | 64/R | 256/R | 1.5 | Indifferent | 1 | Additive |
| PA-99S | 1024/R | 128/R | 512/R | 0.516 | Additive | 0.625 | Additive |
| PA-50S | 256/R | 1024/R | 1024/R | 0.531 | Additive | 0.75 | Additive |
| PA-54S | 1024/R | 512/R | 128/R | 0.625 | Additive | 0.516 | Additive |
| EC-55A | 512/R | 16/S | 1/S | 1 | Additive | 1.031 | Indifferent |
| EC-99A | 256/R | 16/S | 0.5/S | 0.625 | Additive | 1.25 | Indifferent |
| EC-34R | 64/R | 1/S | 0.5/S | 0.625 | Additive | 1.063 | Indifferent |
Abbreviations: FIC index fractional inhibitory concentration index, MEM meropenem, AK amikacin, TGC tigecycline, AB A. baumannii, KP K. pneumoniae, PA P. aeruginosa, EC E. coli
a FIC index was calculated using the lowest concentration of the respective antimicrobial agents at which the lowest value of FIC was achieved. Synergism ≤ 0.5, additive > 0.5—≤ 1, indifference > 1—≤ 4, antagonism > 4 [37]