TABLE 2.
In vitro susceptibility to various aminoglycosides, stratified by gentamicin susceptibility
| Aminoglycoside | Gentamicin susceptible (n = 30)a |
Gentamicin resistant (n = 20)a |
P valuec | ||||||
|---|---|---|---|---|---|---|---|---|---|
| MIC (μg/ml) |
Resistance rate, %b | MIC (μg/ml) |
Resistance rate, %b | ||||||
| Median (range) | 50% | 90% | Median (range) | 50% | 90% | ||||
| Amikacind | 16 (1 to 64) | 16 | 32 | 23 (7/30)d | 16 (4 to 32) | 16 | 16 | 5 (1/20) | NS (0.16) |
| Kanamycin | 256 (2 to >256) | 256 | >256 | 97 (29/30) | 512 (64 to >256) | >256 | >256 | 100 (20/20) | 0.009 |
| Neomycine | 2 (0.5 to 128) | 2 | 64 | NA | 32 (1 to >256) | 32 | 512 | NA | <0.0001 |
| Netilmicin | 64 (0.25 to >64) | 64 | >64 | 97 (29/30) | >64 (32 to >64) | >64 | >64 | 100 (20/20) | 0.032 |
| Plazomicine | 0.25 (0.125 to 1) | 0.25 | 0.5 | NA | 0.5 (0.125 to 1) | 0.5 | 1 | NA | <0.0001 |
| Tobramycin | 16 (0.25 to 32) | 16 | 32 | 97 (29/30) | 32 (16 to >64) | >64 | >64 | 100 (20/20) | 0.008 |
a
Thirty and 20 isolates were susceptible and resistant to gentamicin, respectively. No strain was intermediate to gentamicin. 50% and 90%, MIC50 and MIC90, respectively; NA, not applicable.
b
Numbers in parentheses represent the number with resistance/number tested.
c
P values denote the difference in median MIC of respective aminoglycosides between the gentamicin-susceptible and -resistant isolates. P values were calculated using the Mann-Whitney test. NS, not significant.
d
Amikacin resistance rates include both intermediate and resistant strains.
e
Neomycin and plazomicin interpretive breakpoint MICs have not been established.