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

Abstract

Aims: To overcome contamination and temperature inhibition by isolating campylobacter at 37°C.

Methods: The β 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°C 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°C) had a higher sensitivity for isolating campylobacters: 14 were isolated on AAV compared with 10 on modified CDA (43°C) over three days, and nine were isolated on AAV medium compared with five on modified CDA (43°C) 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°C. Further studies are indicated.