Pilot study for the development of a new campylobacter selective medium at 37 C̊ using aztreonam

Aims: To overcome contamination and temperature inhibition by isolating campylobacter at 37 C̊. Methods: The b lactam antibiotic aztreonam was included in a selective medium because of its inhibitory activity against Gram negative organisms but not against Campylobacter jejuni. Vancomycin and amphotericin were added to inhibit Gram positive bacteria and yeasts. Results: The aztreonam amphotericin vancomycin (AAV) experimental campylobacter selective medium showed growth microaerobically at 37 C̊ of C jejuni, C coli, C lari, C hyointestinalis, C fetus subsp. fetus, and C jejuni subsp. doylei after 24 to 48 hours of incubation. Six campylobacter NCTC strains demonstrated a minimum inhibitory concentration (MIC) > 256 mg/litre for vancomycin and aztreonam, whereas C upsaliensis and two ‘‘campylobacter-like’’ strains now reclassified under genus helicobacter— H cinaedi and H fennelliae—had a MIC of 4 mg/litre for vancomycin and aztreonam. In the pilot study (150 samples), AAV medium (37 C̊) had a higher sensitivity for isolating campylobacters: 14 were isolated on AAV compared with 10 on modified CDA (43 C̊) over three days, and nine were isolated on AAV medium compared with five on modified CDA (43 C̊) after 24 hours of incubation. Contamination rates remained low. Conclusion: The medium was devised in a pilot study performed between 1990 and 1993; however, this is the first report of AAV medium used as a selective medium capable of growing six campylobacters of pathogenic importance at 37 C̊. Further studies are indicated.