Mrs medium

The H. pylori strains ATCC43504 (NCTC11637) and SS1 and thirty clinical isolates were obtained from the Department of Gastroenterology, The First Affiliated Hospital of Nanchang University. The research protocol was approved by the Ethics Committee of the First Affiliated Hospital of Nanchang University (IRB 2018-116). Lactobacillus BG-2-2 and Bifidobacterium WBIN03 were kindly provided by Professor Wei Hua, Sino German Joint Research Institute, Nanchang University. H. pylori strains were maintained on Campylobacter agar base (OXOID, UK) plates supplemented with 5% sheep blood under microaerobic conditions (5% O2, 10% CO2, and 85% N2) at 37°C for 2–3 days. The Lactobacillus strain was grown in MRS medium (Solarbio Technology Co., LTD, Beijing, China) under anaerobic conditions. The Bifidobacterium strain was grown in MRS medium containing 0.05% L-cysteine hydrochloride monohydrate under anaerobic conditions.

B. lactis BL-99 was deposited in the China
Common Microbial Culture Collection and Management Center (CGMCC 15650) on April
26, 2018 [29 (link)] and
identified by 16S rRNA gene amplified using the universal primers 27F
(5’-AGA GTT TGA TCC TGG CTC AG-3’) and 1492R
(5’-GGT TAC CTT GTT ACG ACT T T-3’) [45 (link)]. The standard
B. lactis BL-99 culture was proliferated
with De Man Rogosa Sharpe (MRS) medium (Solarbio, Beijing) supplemented with
0.05% (w/v) L-cysteine (MRSC) for 12–48 hrs at 37°C aerobically [26 (link)] and the anaerobic
environment was obtained with Anaero Gen sachets (Oxoid Ltd., West
Heidelberg/Vic., Australia). Colony-forming unit (CFU) of B.
lactis BL-99 was 1.5*10¹¹ CFU / g and preserved
at -80°C.

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.