Table 2.
Doubling time and antibiotic susceptibility profiles by Etest among N315 and its derived strains
| Strain | Amino acid and/or substitution in RpoB | Doubling time (min)c | MIC (mg/liter)a |
||||||
|---|---|---|---|---|---|---|---|---|---|
| MET | OXA | IPMb | RIF | VAN | DAP | LZD | |||
| N315 | N967 (wild type) | 25.1 ± 0.7 | 1 | 4 | 0.125 | 0.008 | 0.75 | 1.5 | 1 |
| N315ΔIP | N967 (wild type) | 26.7 ± 0.5 | 12 | 8 | 0.25 | 0.008 | 0.75 | 1.5 | 1 |
| ΔIP-H5 | N967I | 30.3 ± 0.9* | >256 | >256 | >32 | 0.004 | 0.75 | 1 | 0.75 |
| ΔIP-H14 | N967 (wild type) | 28.3 ± 1.3 | >256 | >256 | >32 | 0.004 | 2 | 1.75 | 0.75 |
| H5 rpoB(I967N) | N967 (wild type)d | 25.4 ± 1.0 | 6 | 6 | 0.75 | 0.008 | 0.75 | 1 | 0.75 |
| N315 rpoB(N967I) | N967I | 30.2 ± 0.3* | >256 (2–12)b | >256 | >32,(0.05–0.5) | 0.004 | 0.5 | 1.5 | 0.75 |
| N315h4 | R644H | 31.6 ± 2.4* | >256 (0.75–8)b | >256 | >32,(0.02–1.0) | 0.004 | 0.75 | 1 | 0.02 |
a
MET, methicillin; OXA, oxacillin; IPM, imipenem; RIF, rifampin; VAN, vancomycin; DAP, daptomycin; LZD, linezolid.
b
Eagle-type resistance was observed as the growth of the strain was inhibited at the drug concentrations shown in parentheses (Fig. 2).
c
The level of significance was determined by a two sided Student t test (*, P < 0.012) in the comparison of rpoB mutants and wild-type rpoB strains.
d
Revertant strain.