Evaluation of selective media for the isolation of Brachyspira aalborgi from human faeces

Abstract

The purposes of this study were to identify a solid medium that supports improved growth of the anaerobic intestinal spirochaete Brachyspira aalborgi, to modify this for use as a selective isolation medium and then to test the medium for its effectiveness in isolating B. aalborgi from patients’ faeces. Of the media evaluated, brain heart infusion agar (BHIA) with 10 % bovine blood (BB) was the most effective base–supplement combination for growth, with colonies attaining 1.2 mm in diameter by 21 days. Incubation in an anaerobic jar (94 % H2, 6 % CO2) permitted growth of larger colonies than incubation in an anaerobic chamber (80 % N2, 10 % H2, 10 % CO2). Growth was improved only slightly at 38.5 °C compared with 37 °C. Selection of B. aalborgi from artificially seeded faeces was achieved equally well on eight different solid media containing spectinomycin (400 μg ml−1) alone or in combinations with polymyxin B (5 μg ml−1), colistin (25 μg ml−1) and rifampicin (12.5 μg ml−1). By using BHIA 10 % BB with spectinomycin plus polymyxin B, B. aalborgi was isolated from one of five human faecal samples that were positive for B. aalborgi by PCR amplification. This is the first report of the isolation of B. aalborgi from human faeces.