Establishment of a Mouse Model of DSS-Induced Colitis

Male BALB/c mice at 6–8 weeks old were purchased from Guangdong Medical Laboratory Animal Center (GDMLAC; certificate number SYXK 2013-0002, Foshan, China). The mice were housed in a specific pathogen-free room with a 12-h light/dark cycle, consistent temperature (24°C), and humidity (50–70%) and allowed free access to food and water. The experimental procedures were approved by the Animal Ethics Committee of Guangzhou First People’s Hospital (acceptance no. 2017-202).

The mice were randomized and fed with regular water as the control or water containing 2.5% DSS (Sigma, United States) every other week for 5 weeks to induce colitis (Wirtz et al., 2007; Jiang et al., 2020). The mice were divided into four groups: the control, the DSS colitis model, the human FMT, and the mouse FMT groups. The control (n = 5) and DSS colitis model groups (n = 6) were administrated with phosphate buffered saline (PBS, 0.1 ml/10 g) by gavage. The human FMT group was fed with fresh human FM (0.1 ml/10 g) prepared from the same healthy donor, whereas the mouse FMT group was fed with fresh mouse FM prepared from healthy mice (n = 6 per group). The experimental protocols were illustrated in the schematic diagram (Figure 1A). The mice were monitored daily for their body weights, stool consistency, and the presence of blood in the anus or stool. At the end of the experiment, their blood and stool samples were collected, and their colon tissues were dissected. The colon lengths were measured, and the dissected tissues were fixed overnight in 10% neutral buffered formalin. Their serum samples were prepared for ELISA assays.

FMT with the gut microbiota from healthy donors or mice significantly ameliorates clinical symptoms and inflammation in colitis mice. BALB/c mice were randomized and fed with normal water as the control or water containing 2.5% DSS to induce colitis. The control and some DSS-fed mice (DSS group, n = 6) were fed with PBS, whereas other DSS-fed mice were fed with fresh human or mouse fecal microbiota as the DSS + FMT_h or DSS + FMT_m group (n = 6 per group). (A) Schematic diagram of the experimental design. The degrees of red colors indicate the severity of colitis. (B) The dynamics of Disease Activity Index (DAI) in each group. (C) Mouse colon lengths in each group. (D) The levels of serum IL-6. (E) The levels of serum TNF-α. Data are individual means or the mean ± SD of each group from three separate experiments. *p < 0.05, **p < 0.01, ***p < 0.001.