Table 1.
Disc susceptibility assay for K. pneumoniae NCTC 5055 transformants expressing regulator genes
| Antibiotic (μg in disc) | pBAD (control) zone (mm) | pBAD(marA) zone (difference from control) (mm) | pBAD(soxS) zone (difference from control) (mm) | pBAD(rarA) zone (difference from control) (mm) | pBAD(ramA) zone (difference from control) (mm) | ECL8ΔramR zone (difference from ECL8) (mm) |
|---|---|---|---|---|---|---|
| Amikacin (30) | 24 (S) | NC | NC | NC | NC | NC (S) |
| Gentamicin (10) | 23 (S) | NC | NC | NC | NC | −2 (S) |
| Tobramycin (10) | 22 (S) | −2 (S) | NC | −2 (S) | NC | NC (S) |
| Cefoxitin (30) | 23 (S) | NC | −2 (S) | −2 (S) | −6 (I) | −4 (S) |
| Cefuroxime (30) | 22 (S) | NC | NC | −2 (S) | −5 (I) | −9 (I) |
| Ceftriaxone (30) | 32 (S) | NC | NC | −2 (S) | −3 (S) | −7 (S) |
| Cefotaxime (30) | 35 (S) | NC | −2 (S) | NC | −6 (S) | −4 (S) |
| Ceftazidime (30) | 29 (S) | NC | −2 (S) | −2 (S) | −4 (S) | −5 (S) |
| Cefepime (30) | 30 (S) | NC | NC | NC | −4 (S) | −3 (S) |
| Aztreonam (30) | 34 (S) | −3 (S) | −2 (S) | −4 (S) | −6 (S) | −2 (S) |
| Imipenem (10) | 29 (S) | NC | NC | NC | −2 (S) | NC (S) |
| Meropenem (10) | 31 (S) | NC | NC | NC | NC | NC (S) |
| Doripenem (10) | 30 (S) | NC | NC | NC | NC | NC (S) |
| Ciprofloxacin (5) | 30 (S) | NC | NC | NC | −8 (S) | −3 (S) |
| Norfloxacin (10) | 30 (S) | NC | −2 (S) | −3 (S) | −11 (S) | −9 (S) |
| Ofloxacin (5) | 28 (S) | NC | NC | −3 (S) | −5 (S) | −9 (S) |
| Tigecycline (15) | 21 | NC | NC | −2 | −4 | −5 |
| Minocycline (30) | 21 (S) | NC | NC | NC | −4 (S) | −6 (S) |
| Chloramphenicol (30) | 25 (S) | NC | NC | −3 (S) | −6 (S) | −9 (S) |
| Trimethoprim/sulfamethoxazole (1.25/23.75) | 27 (S) | NC | NC | NC | −4 (S) | NC (S) |
S, susceptible; I, intermediate resistant; NC, no change in zone diameter versus control.
Assays were performed using Mueller–Hinton agar with 0.2% (w/v) arabinose to stimulate expression of the cloned genes and 50 mg/L ampicillin to select for the pBAD plasmids. Otherwise, the assay was performed according to the CLSI protocol.17
Values reported are the means of at least three repetitions rounded to the nearest integer.
Mean changes <2 mm are reported as NC.
Susceptibility breakpoints are as set by the CLSI.20