Table 5.
Minimal inhibitory concentration of β-lactams against E. coli strains harboring various plasmids*.
β-lactam |
Inducer† |
Strains |
|||||||
|---|---|---|---|---|---|---|---|---|---|
BW25113 |
BW25113pJEH12(ycbB) |
M1cured |
M1curedpJEH12(ycbB) |
BW25113pKT8(relA') |
BW25113pKT8(relA')pKT2(ycbB) |
BW25113ΔrelApKT8(relA') |
BW25113ΔrelApKT8(relA')pKT2(ycbB) |
||
|
Ampicillin |
None |
8 |
8 |
8 |
8 |
8 |
4 |
8 |
4 |
IPTG |
8 |
8 |
8 |
128 |
8 |
4 |
8 |
4 |
|
Ara |
8 |
8 |
8 |
8 |
8 |
8 |
8 |
4 |
|
IPTG+Ara |
8 |
8 |
8 |
128 |
8 |
64 |
8 |
128 |
|
|
Ceftriaxone |
None |
0,05 |
0,05 |
0,05 |
0,05 |
0,05 |
0,05 |
0,05 |
0,05 |
IPTG |
0,05 |
0,05 |
0,05 |
32 |
0,05 |
0,05 |
0,05 |
0,05 |
|
Ara |
0,05 |
0,05 |
0,05 |
0,05 |
0,05 |
0,1 |
0,05 |
0,05 |
|
IPTG+Ara |
0,05 |
0,05 |
0,05 |
32 |
0,05 |
32 |
0,05 |
32 |
|
*Minimal inhibitory concentrations were determined by the agar dilution method with an inoculum of 105 colony forming units per spot in brain heart infusion agar after 24 hr of incubation at 37°C. The same results were obtained with 104 and 106 colony forming units, indicating that YcbB in combination with elevated (p)ppGpp rendered the bulk of the population resistant.
†Induction was performed with 50 mM IPTG, 1% arabinose (Ara), and a combination of both inducers (IPTG+Ara). IPTG induces expression of the ycbB gene of plasmids pJEH12(ycbB) and pKT2(ycbB). Arabinose induces expression of relA’ encoding the first 455 residues of RelA.