TABLE 1.
MICs of different antimicrobials and ESBL test results for the clinical strain K. pneumoniae NK29, its plasmid pK29 transconjugant E. coli J53/pK29, and the reference strain E. coli J53
| Antimicrobial agent | MIC (μg/ml)a
|
Zone of inhibition (mm) by disk diffusion test
|
||||
|---|---|---|---|---|---|---|
| K. pneumoniae NK29 | E. coli J53/pK29 transconjugant | E. coli J53 | K. pneumoniae NK29 | E. coli J53/pK29 transconjugant | E. coli J53 | |
| Aminoglycosides | ||||||
| Gentamicin | 3 | 1.5 | 0.25 | |||
| Kanamycin | 32 | 32 | 8 | |||
| β-Lactams | ||||||
| Amoxicillin-clavulanic acid | 48 | 48 | 8 | |||
| Aztreonam | 4 | 2 | 0.064 | |||
| Cefepime | 2 | 1 | 0.094 | |||
| Cefotaxime | 32 | 24 | 0.064 | |||
| Cefoxitin | >256 | >256 | 4 | |||
| Ceftazidime | 16 | 1.5 | 0.19 | |||
| Ceftriaxone | 24 | 16 | 0.19 | |||
| Imipenem | 0.25 | 0.25 | 0.25 | |||
| Other drugs | ||||||
| Chloramphenicol | 96 | 96 | 4 | |||
| Ciprofloxacin | 0.047 | 0.012 | 0.012 | |||
| Sulfamethoxazole | >512 | >512 | ≤64 | |||
| Tetracycline | 8 | 2 | 2 | |||
| Trimethoprim-sulfamethoxazole | 0.50 | 0.064 | 0.047 | |||
| Drugs for ESBL testingb | ||||||
| CAZ/CAZ + CLA | 16/>4.0 | 1.5/1.0 | <0.5/0.25 | |||
| CTX/CTX + CLA | >16/>1.0 | >16/>1.0 | <0.25/0.064 | |||
| CAZ vs CAZ + CLA | 17 vs 17 | 27 vs 27 | 33 vs 33 | |||
| CTX vs CTX + CLA | 13 vs 15 | 16 vs 17 | 31 vs 31 | |||
a
Based on Etest results, except for kanamycin and sulfamethoxazole MICs, which are from broth microdilution tests. For sulfamethoxazole, the lowest concentration tested was 64 μg/ml, and thus the actual MIC for J53 could be lower.
b
CAZ, ceftazidime; CTX, cefotaxime; CLA, clavulanic acid. The ceftazidime results were all negative, and the cefotaxime results were indeterminate for NK29 and the J53/pK29 transconjugant based on MIC results. The isolates all tested negative for ESBLs by the CLSI disk diffusion confirmatory test (5).