Vinyl anaerobic airlock chamber

All experimental procedures were carried out in a vinyl anaerobic airlock chamber (Coy Laboratory Products, Grass Lake, MI, USA), with an atmosphere composed of N₂, H₂, and CO₂ (but depleted in oxygen). Fecal samples were obtained from two healthy volunteers (two males aged 30 and 60 years) who had provided verbal informed consent. Then, 0.5 g fecal samples were immediately suspended in 4.5 mL anaerobic phosphate‐buffered solution containing KH₂PO₄ (4.5 g), Na₂HPO₄ (6.0 g), L‐cysteine·HCl·H₂O (0.5 g), Tween^® 80 (0.5 g), and agar (1.0 g) per 1 L distilled water. Approximately 50 µL fecal samples at 10⁷‐ and 10⁸‐fold dilutions were plated on BL and TYG agar. After 2 days (BL agar) and 7 days (TYG agar) of incubation under anaerobic conditions at 37°C, the colonies on these agars were counted and selected as living cells. The percentage of recovery was calculated as (average colony count on upper layer/average total colony count) × 100.