Table 1.
Checkerboard assay for CST-Ga(III) interactions in MH broth and M9-DIP with a selected panel of A. baumannii strainsa
| Strain | MH broth |
M9-DIP |
||||||
|---|---|---|---|---|---|---|---|---|
| Effect (FICI value) of combinationb | MIC |
Effect (FICI value) of combination | MIC |
|||||
| CST (μg/ml)c | Ga(NO3)3 (μM) | CST (μg/ml)-Ga(NO3)3 (μM) | CST (μg/ml) | Ga(NO3)3 (μM) | CST (μg/ml)-Ga(NO3)3 (μM) | |||
| ATCC 19606T | Sy (≤0.26) | 0.5 | ≥256 | 0.125–2 | Sy (0.31) | 2 | 8 | 0.125–2 |
| ATCC 17978 | Sy (≤0.13) | 1 | ≥256 | 0.125–2 | Sy (0.28) | 4 | 64 | 1–2 |
| RUH 875 | Sy (≤0.19) | 1 | ≥256 | 0.125–16 | Sy (0.25) | 4 | 64 | 0.5–8 |
| RUH 134 | Sy (≤0.16) | 2 | ≥256 | 0.25–8 | Sy (0.16) | 4 | 64 | 0.5–2 |
| RUH 5875 | Sy (≤0.14) | 1 | ≥256 | 0.125–4 | Sy (0.50) | 4 | 16 | 1–4 |
| AYE | Sy (≤0.14) | 1 | ≥256 | 0.125–4 | Sy (0.25) | 4 | 16 | 0.5–2 |
| ACICU | Sy (≤0.26) | 1 | ≥256 | 0.25–2 | Sy (0.37) | 8 | 32 | 1–4 |
| 50C | Sy (≤0.26) | 16 | ≥256 | 4–2 | Sy (0.13) | 256 | 64 | 2–8 |
| A371 | Sy (≤0.26) | 1 | ≥256 | 0.25–2 | Sy (0.25) | 4 | 64 | 0.5–8 |
a
MICs for drug(s) alone and in effective synergistic combination, measured after 18 h growth in MH or 48 h growth in M9-DIP.
b
In order to calculate the FICI, the MIC of Ga(NO3)3 in MH broth was assumed to be ≥256 μM for all strains.
c
Breakpoint criteria for CST in MH broth were susceptible, ≤2 mg/liter, and resistant, ≥4 mg/liter (26).