TABLE 1.
MICs (μg/ml) of imipenem and colistin against blaVIM-1-type MBL-producing K. pneumoniae isolates and in vitro interaction of the combination
| Strain | MIC (μg/ml)
|
Presence of ESBL | Interactiona (time of growth [h]) | No. of isolates showing synergy (or antagonism, if indicated)/total no. of isolates (%) | |
|---|---|---|---|---|---|
| Imipenem | Colistin | ||||
| Imipenem- and colistin-susceptible isolates | 3/8 (37.5) | ||||
| 716 | 3 | 0.25 | Yes | Indifference | |
| 631 CΙ | 0.75 | 0.38 | Yes | Synergy (24)b | |
| 2596 II | 2 | 0.5 | Yes | Synergy (24)b | |
| 1057 Β ΙΙ | 1.5 | 0.5 | Yes | Indifference | |
| 757 | 1 | 0.25 | Yes | Synergy (3, 5, 24)b | |
| 270 E ΙΙ | 1.5 | 0.25 | Yes | Indifference | |
| 2354 | 2 | 0.25 | Yes | Indifference | |
| 1037 E ΙΙ | 2 | 0.38 | Yes | Indifference | |
| Non-imipenem-susceptible and colistin-susceptible isolates | 9/16 (56.3) | ||||
| 350 I | 6 | 0.5 | No | Synergy (1, 24)c | |
| 498 II | 8 | 0.3 | Yes | Synergy (24)c | |
| 1587 I | >32 | 0.5 | Yes | Synergy (24)c | |
| 266 E | >32 | 0.4 | Yes | Indifference | |
| 1526 | 24 | 0.4 | No | Synergy (24)c | |
| 760 C | >32 | 0.4 | No | Synergy (24)c | |
| 329 Β Ι | >32 | 0.2 | Yes | Synergy (24)c | |
| 175 ΙΙΙ | >32 | 0.3 | Yes | Indifference | |
| 4412 Β ΙΙ | >32 | 0.5 | Yes | Indifference | |
| 377 II | >32 | 0.5 | Yes | Synergy (5c or 5 and 24d) | |
| 513 E I | >32 | 0.38 | Yes | Indifference | |
| 682 E I | >32 | 0.19 | Yes | Synergy (24)c,d | |
| 735 E II | >32 | 0.38 | Yes | Indifference | |
| 1437 B II | >32 | 0.5 | Yes | Synergy (24)c | |
| 761 E I | >32 | 0.2 | Yes | Indifference | |
| 332 E | >32 | 0.25 | Yes | Indifference | |
| Non-imipenem-susceptible and non-colistin-susceptible isolates | 7/15 (46.7) (antagonism), 2/15 (13.3) (synergy) | ||||
| 748 A IV | >32 | 48 | Yes | Indifference | |
| 231 D | >32 | 48 | Yes | Antagonism (3, 5)d | |
| 1171 C II | 12 | 256 | Yes | Indifference | |
| 1014 A I | >32 | 96 | Yes | Antagonism (5)d | |
| 1459 | >32 | 256 | Yes | Antagonism (3, 5)d | |
| 1057 A | >32 | 48 | Yes | Antagonism (5)d | |
| 1326 A | >32 | 96 | Yes | Antagonism (3, 5)d | |
| 712 B I | 24 | 16 | No | Indifference | |
| 1478 C I | 8 | 128 | Yes | Antagonism (3, 5)d | |
| 4090 B | 12 | 32 | Yes | Indifference | |
| 1110 B II | 6 | 64 | Yes | Antagonism (24)d | |
| 674 C II | >32 | 3 | No | Synergy (3, 5, 24)d | |
| 963 II | >32 | 4 | No | Indifference | |
| 1919 | >32 | 4 | Yes | Synergy (24)d | |
| 680 A | >32 | 4 | No | Indifference | |
| Imipenem-susceptible and non-colistin-susceptible isolates | 3/3 (100) (antagonism) | ||||
| 1119 | 2 | 48 | Yes | Antagonism (3,e 5d) | |
| 318 G Ι | 3 | 24 | Yes | Antagonism (24)d | |
| 240 Β Ι | 4 | 64 | Yes | Antagonism (24)d | |
a
All combinations tested at all time points exhibited indifference unless otherwise specified.
b
Concentrations tested were as follows: imipenem and colistin, 4× MIC.
c
Concentrations tested were as follows: imipenem, 10 μg/ml; and colistin, 4× MIC.
d
Concentrations tested were as follows: imipenem, 10 μg/ml; and colistin, 5 μg/ml.
e
Concentrations tested were as follows: imipenem, 4× MIC; and colistin, 5μg/ml.