Antimicrobial susceptibility testing of 59 strains of Campylobacter fetus subsp. fetus.

The susceptibilities of 59 Campylobacter fetus subsp. fetus isolates to eight antibiotics were studied by the agar dilution, E-test, and disk diffusion methods. None of the isolates were beta-lactamase producers. All were susceptible to ampicillin, gentamicin, imipenem, and meropenem as determined by the three methods, with MICs at which 90% of the isolates are inhibited (MIC90s) (determined by agar dilution) of 2, 1, < or = 0.06, and 0.12 microgram/ml, respectively. Twenty-seven percent of the isolates were resistant to tetracycline, with complete agreement between the agar dilution and disk diffusion results. The MIC90s determined by agar dilution were 2 micrograms/ml for erythromycin, 1 microgram/ml for ciprofloxacin, and 8 micrograms/ml for cefotaxime.