Susceptibility testing of Campylobacter fetus subsp. jejuni, using broth microdilution panels

Twenty-five isolates of Campylobacter fetus subsp. jejuni were tested by broth microdilution panels (Sensititre; GIBCO Diagnostics, Chagrin Falls, Ohio) and the minimal inhibitory concentrations (MICs) were compared with the corresponding MICs obtained by the standard agar dilution technique. Microdilution panels designed for testing gram-positive organisms were used so that erythromycin, the antibiotic of choice for this organism, could be included. The correlation with agar dilution was relatively poor when Mueller-Hinton broth was used; the MICs that were within one twofold dilution of the corresponding agar dilution MIC ranged from 15% with tetracycline to 75% with ampicillin. The overall agreement for all antibiotics tested was 48%. The correlation improved significantly, however, to an overall agreement of 87% when Wilkins-Chalgren broth was substituted in the broth microdilution procedure. Our results indicate that the broth microdilution test is an accurate method for testing this organism, provided than an appropriate medium is used.