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

The purposes of this study were to identify a solidmedium that supports improved growth of the anaerobic intestinal spirochaete Brachyspira aalborgi, to modify this for use as aselective isolation medium and then to test the medium for its effectiveness inisolating B. aalborgi from patients’ faeces. Ofthe media evaluated, brain heart infusion agar (BHIA) with 10 % bovine blood(BB) was the most effective base–supplement combination for growth, withcolonies attaining 1.2 mm in diameter by 21 days. Incubation in an anaerobicjar (94 % H₂, 6 % CO₂) permitted growth of larger coloniesthan incubation in an anaerobic chamber (80 % N₂, 10 % H₂, 10 % CO₂). Growth was improved only slightly at 38.5 °C comparedwith 37 °C. Selection of B. aalborgi from artificiallyseeded faeces was achieved equally well on eight different solid mediacontaining 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 spectinomycinplus polymyxin B, B. aalborgi was isolated fromone of five human faecal samples that were positive for B.aalborgi by PCR amplification. This is the first report of the isolationof B. aalborgi from human faeces.