Table 2.
Combined disk test for colistin in combination with pterostilbene for each of the tested bacterial isolates.
| Specices | Inhibition zone diameter (mm) | |||||
|---|---|---|---|---|---|---|
| Assay | Colistin (10 μg) | Colistin (10 μg) + Pterostilbene (8 μg/mL) | Increase | Colistin (10 μg) + Pterostilbene (32 μg/mL) | Increase | |
| K. pneumoniae ZJ05 | Assay 1 | 8.5 | 11.5 | 3 | 13.0 | 4.5 |
| Assay 2 | 9.5 | 11.5 | 2.0 | 14.0 | 4.5 | |
| Assay 3 | 9.0 | 11.0 | 2.0 | 14.0 | 5.0 | |
| Mean | 9.0 ± 0.50 | 11.33 ± 0.29** | 2.33 ± 0.58 | 13.67 ± 0.58** | 4.67 ± 0.29 | |
| K. pneumoniae ZJ02 | Assay 1 | 9.5 | 11.0 | 1.5 | 13.5 | 4 |
| Assay 2 | 9.0 | 10.5 | 1.5 | 13.5 | 4.5 | |
| Assay 3 | 9.0 | 11.0 | 2 | 13.5 | 4.5 | |
| Mean | 9.17 ± 0.29 | 10.83 ± 0.29** | 1.67 ± 0.29 | 13.50 ± 0.00** | 4.33 ± 0.29 | |
| E. coli DH5α (pUC19-mcr-1) | Assay 1 | 10.5 | 12.0 | 1.5 | 13.5 | 3.0 |
| Assay 2 | 10.0 | 11.0 | 1.0 | 13.0 | 3.0 | |
| Assay 3 | 11.0 | 11.5 | 0.5 | 13.0 | 2.0 | |
| Mean | 10.0 ± 0.50 | 11.50 ± 0.50 | 1.00 ± 0.50 | 13.17 ± 0.29** | 2.67 ± 0.58 | |
| E. coli ATCC 25922 | Assay 1 | 13.0 | 13.5 | 0.5 | 13.5 | 0.5 |
| Assay 2 | 12.5 | 13.5 | 1.0 | 12.0 | -0.5 | |
| Assay 3 | 13.0 | 13.0 | 0.0 | 13.5 | 0.5 | |
| Mean | 12.83 ± 0.89 | 13.33 ± 0.29 | 0.50 ± 0.50 | 13.00 ± 0.87 | 0.17 ± 0.58 | |
The combined disk test method was performed in triplicate. Three 10-μg colistin disks with pterostilbene (0, 8, and 32 μg/mL) were used.
**
P < 0.01 compared with the colistin 10-μg disk alone based on two-tailed Student's t-tests. The mean inhibition zone diameter of all isolates were indicated in italics, and the increased values were indicated in bold.