Table 1.

Susceptibilities of 59 strains of C. fetussubsp. fetus as determined by agar dilution, disk diffusion, or E test

AntibioticMethodBreakpoint for susceptible strainsa% SusceptibleDisk diameter for susceptibleb organism (mm)MIC (μg/ml)
Range50%90%
AmpicillinAgar dilution≤81000.25–812
E test≤81000.5–212
Disk diffusion≥1710018–60
GentamicinAgar dilution≤41000.12–10.51
E test≤41000.5–212
Disk diffusion≥1510027–48
ImipenemAgar dilution≤4100≤0.06≤0.06≤0.06
E test≤41000.03–0.250.060.06
Disk diffusion≥1610041–74
MeropenemAgar dilution≤4100≤0.06–0.25≤0.060.12
E test≤41000.03–0.50.060.12
Disk diffusion≥1410036–54
CefotaximeAgar dilution≤8904–1688
E test≤8016–646464
Disk diffusion≥238420–50
ErythromycinAgar dilution≤0.5390.12–412
Disk diffusion≥2310032–54
TetracyclineAgar dilution≤473≤0.06–≥128≤0.06≥128
Disk diffusion≥197336–71
CiprofloxacinAgar dilution≤198≤0.06–20.51
Disk diffusion≥2110023–46
  • a Breakpoints are those established by the NCCLS (20, 21) in micrograms per milliliter for agar dilution and the E test and in millimeters for disk diffusion for organisms that grow aerobically. The breakpoints of strains susceptible to meropenem are those established by Zeneca Pharma Inc.

  • b Determined by agar dilution.