TABLE 2.
Antibiotic susceptibilities of E. coli and S. enterica serovar Typhimurium strains
| Strain | Zone of inhibition (mm)a
|
||||
|---|---|---|---|---|---|
| NAL | CIP | CHL | TET | GEN | |
| S. enterica serovar Typhimurium | |||||
| 14028s | 40 ± 1 | 48 ± 2 | 41 ± 1 | 42 ± 2 | NDd |
| 14028s ΔramA | 38 ± 1 | 47 ± 2 | 40 ± 1 | 42 ± 2 | ND |
| 14028s + pTrcHisA-ramAb | |||||
| No IPTG | 21 ± 1 | 40 ± 2 | 29 ± 1 | 37 ± 1 | ND |
| IPTG added | 15 ± 1 | 33 ± 1 | 12 ± 2 | 30 ± 2 | ND |
| E. coli | |||||
| MC1061 + pB1c | ND | 42 ± 2 | 30 ± 2 | ND | ND |
| MC1061 + pB1-ramA | ND | 32 ± 1 | 24 ± 2 | ND | ND |
| AG100 | 23 ± 1 | 39 ± 1 | 35 ± 1 | 31 ± 1 | 30 ± 1 |
| AG100kana (marA::kan) | 23 ± 1 | 41 ± 2 | 35 ± 1 | 30 ± 1 | 30 ± 1 |
| AG100 + pHisA-ramA | |||||
| No IPTG | 21 ± 1 | 39 ± 1 | 34 ± 1 | 30 ± 1 | 30 ± 1 |
| IPTG added | 15 ± 1 | 36 ± 1 | 21 ± 2 | 27 ± 1 | 30 ± 1 |
| AG100kana (marA::kan) + pHisA-ramA | |||||
| No IPTG | 23 ± 1 | 40 ± 1 | 34 ± 2 | 30 ± 1 | 30 ± 1 |
| IPTG added | 17 ± 1 | 33 ± 1 | 22 ± 1 | 25 ± 1 | 30 ± 1 |
a
Zones of growth inhibition around cotton disks (diameters, 6 mm) were determined by the disk diffusion assay on standardized M9 minimal medium agar plates; the following dosages were added to the disks: nalidixic acid (NAL), 130 μg; ciprofloxacin (CIP) 10 μg; chloramphenicol (CHL), 300 μg; tetracycline (TET), 80 μg; gentamicin (GEN), 100 μg. The (CIP), mean and standard deviations of four independent experiments are given.
b
ramA gene expressed on IPTG-inducible plasmid pTrcHisA (Invitrogen).
c
pB1, plasmid pBluescript.
d
ND, not done.