Clostridium sporogenes

L. reuteri I5007 was isolated from the colonic mucosa of healthy weaning piglets and further confirmed through whole-genome sequencing (NCBI ID: 1340495); this strain was found to be chloramphenicol, kanamycin, and streptomycin-resistant. L. reuteri I5007, mutant L. reuteri I5007, L. johnsonii, L. plantarum, L. delbrueckii, and L. rhamnosus GG were cultured in MRS medium (Solarbio Science and Technology Co., Beijing, China) at 37 ℃ for 20 h under anaerobic conditions. Bacterial cells were collected by centrifugation at 12,000 rpm for 15 min. Heat-killed L. reuteri I5007 was prepared by heating at 95 °C for 20 min. No colonies were detected after 48 h of culture at 37 °C after heat treatment. Clostridium sporogenes (ATCC 15579; American Type Culture Collection) was cultured in fluid thioglycolate medium in an anaerobic atmosphere at 37 °C for 24 h. C. rodentium (ATCC 51459; American Type Culture Collection) was inoculated into LB broth and cultured in a shaker overnight at 37 °C. Overnight culture was then centrifuged at 12,000 rpm for 15 min, washed once, and resuspended at 10⁸ CFU/mL in PBS. L. reuteri I5007 was cultured anaerobically with or without tryptophan at 0.01, 0.1, or 1 mM at 37 °C for 20 h prior to measurement of indole derivatives in the supernatant.