Table 2

Doubling time and antibiotic susceptibility profiles by Etest among N315 and its derived strains

StrainAmino acid and/or substitution in RpoBDoubling time (min)cMIC (mg/liter)a
METOXAIPMbRIFVANDAPLZD
N315N967 (wild type)25.1 ± 0.7140.1250.0080.751.51
N315ΔIPN967 (wild type)26.7 ± 0.51280.250.0080.751.51
ΔIP-H5N967I30.3 ± 0.9*>256>256>320.0040.7510.75
ΔIP-H14N967 (wild type)28.3 ± 1.3>256>256>320.00421.750.75
H5 rpoB(I967N)N967 (wild type)d25.4 ± 1.0660.750.0080.7510.75
N315 rpoB(N967I)N967I30.2 ± 0.3*>256 (2–12)b>256>32,(0.05–0.5)0.0040.51.50.75
N315h4R644H31.6 ± 2.4*>256 (0.75–8)b>256>32,(0.02–1.0)0.0040.7510.02
  • 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.