Bacterial cultures
The P.g strain (American Type Culture Collection, no. ATCC33227) was grown in Columbia Agar Base (Shanghai Solarbio Science & Technology Co., Ltd., China) under anaerobic conditions at 37 °C for 3 d. Then, theP.g was grown in BHI (Shanghai Solarbio Science & Technology Co., Ltd., China) broth supplemented with vitamin K (0.5 μg/ml), protohemin (5 μg/ml), yeast powder (1 mg/ml) and cysteine (0.05%). After centrifugation and the removal of the media, the cells were washed three times with phosphate-buffered saline (PBS, Shanghai Solarbio Science & Technology Co., Ltd.). Finally, 200 μL (109/mL CFU) was administered to each mouse in theP.g group.