Table 1.
Minimum inhibitory concentrations (MICs) and fractional inhibitory concentration (FIC) index of blaIMP-1 or blaIMP-6 positive Enterobacteriaceae isolates
| Isolates | MIC (μg/mL) | MEM MIC reduction | FIC index | Evaluation | |||
|---|---|---|---|---|---|---|---|
| MEM | CMZ | ||||||
| IMP-1 producing isolates | TUM10695 | E. hormaechei | 2 | 512 | 1/4, 1/8 | 0.27, 0.19 | Synergy |
| TUM11051 | E. hormaechei | 8 | 2048 | 1/4, 1/4 | 0.50, 0.50 | Synergy | |
| TUM11052 | E. hormaechei | 8 | 1024 | 1/4, 1/4 | 0.28, 0.27 | Synergy | |
| TUM11134 | E. hormaechei | 2 | 1024 | 1/4, 1/4 | 0.31, 0.50 | Synergy | |
| TUM11259 | E. coli | 8 | 512 | 1/8, 1/8 | 0.25, 0.38 | Synergy | |
| TUM13773 | E. coli | 4 | 256 | 1/4, 1/8 | 0.50, 0.37 | Synergy | |
| TUM14683 | E. coli | 4 | 512 | 1/16, 1/8 | 0.19, 0.19 | Synergy | |
| TUM14697 | E. coli | 2 | 64 | 1/4, 1/8 | 0.38, 0.19 | Synergy | |
| TUM14759 | E. coli | 4 | 512 | 1/8, 1/4 | 0.25, 0.28 | Synergy | |
| TUM13774 | K. pneumoniae | 8 | 256 | 1/8, 1/8 | 0.25, 0.38 | Synergy | |
| TUM13775 | K. pneumoniae | 8 | 512 | 1/8, 1/8 | 0.25, 0.25 | Synergy | |
| TUM14366 | K. pneumoniae | 8 | 256 | 1/8, 1/4 | 0.25, 0.31 | Synergy | |
| TUM14380 | K. pneumoniae | 2 | 512 | 1/4, 1/4 | 0.50, 0.38 | Synergy | |
| IMP-6 producing isolates | E015 | E. coli | 16 | 256 | 1/8, 1/16 | 0.16, 0.13 | Synergy |
| E020 | E. coli | 16 | 256 | 1/8, 1/16 | 0.13, 0.19 | Synergy | |
| E030 | E. coli | 32 | 512 | 1/16, 1/16 | 0.09, 0.08 | Synergy | |
| E038 | E. coli | 16 | 512 | 1/32, 1/16 | 0.05, 0.14 | Synergy | |
| E046 | E. coli | 32 | 1024 | 1/8, 1/8 | 0.14, 0.14 | Synergy | |
| E070 | E. coli | 16 | 256 | 1/32, 1/32 | 0.19, 0.06 | Synergy | |
| E109 | E. coli | 16 | 64 | 1/32, 1/32 | 0.28, 0.28 | Synergy | |
| E138 | E. coli | 64 | 1024 | 1/8, 1/8 | 0.19, 0.19 | Synergy | |
| E039 | K. pneumoniae | 32 | 256 | 1/16, 1/16 | 0.13, 0.13 | Synergy | |
| E045 | K. pneumoniae | 32 | 256 | 1/8, 1/16 | 0.16, 0.09 | Synergy | |
| E065 | K. pneumoniae | 32 | 256 | 1/32, 1/32 | 0.09, 0.06 | Synergy | |
| E085 | K. pneumoniae | 32 | 512 | 1/8, 1/8 | 0.19, 0.16 | Synergy | |
| E139 | K. pneumoniae | 32 | 1024 | 1/8, 1/4 | 0.25, 0.27 | Synergy | |
CMZ cefmetazole, MEM meropenem
FIC index was measured in duplication. FIC index was calculated in following formula; FIC index = (MIC of MEM measured in combination with CMZ)/(MIC of MEM only) + (MIC of CMZ measured in combination with MEM)/(MIC of CMZ only). FIC index ≤ 0.5 was defined as synergy, > 0.5 to ≤ 4.0 as indifferent, and > 4.0 as antagonistic. MEM MIC fold-reduction by CMZ was calculated at the lowest FIC index