Oral supplementation of heat-killed Enterococcus faecalis strain EC-12 relieves gastrointestinal discomfort and alters the gut ecosystem in academically stressed students

Stress significantly impacts both gastrointestinal and mental health and the gut microbiota playing a pivotal role in this process. Enterococcus faecalis strain EC-12 (EC-12) is a lactic acid bacterium with several benefits to health. To investigate the impact of oral supplementation with heat-killed EC-12 on the discomfort caused by stress, a randomized, double-blind, placebo-controlled trial was conducted, with students under academic stress taking EC-12(n=14) or a placebo(n=13) daily for one week. The improvement of students' symptoms was assessed through the Visual Analog Scale (VAS) questionnaire. Fecal microbiota were characterized by next generation sequencing of 16S rRNA genes and the fecal metabolite and short chain fatty acids were analyzed by non-targeted GC-MS metabolomics approach. No significant differences in salivary cortisol levels and psychological discomfort symptoms were observed among students from two groups before and after the trial. Significant improvements in abdominal pain and rumbling stomach were found in the EC-12 group compared to the placebo group and no changes were observed in salivary cortisol levels and mental symptoms. The main composition and diversity of gut microbiota is not significantly changed. The relative abundance of Enterococcus genus significantly increased in the post-EC-12 group. Functional analysis based on gut microbiota data suggested that EC-12 intake alters certain metabolic pathways. Fecal microbiota metabolomic analysis indicates that EC-12 intake alters the composition of fecal metabolites, with a significant increase in tryptamine levels compared to before the trial. The levels of fecal short-chain fatty acids did not show significant changes between different groups before and after the trial. The ratio of students with symptoms improving among those with tryptamine increased were calculated based on the number of students with symptomatic improvements among students with elevated fecal tryptamine levels is higher in rumbling stomach compared with other digestive discomfort feelings. These results suggest that oral supplementation of EC-12 has a potential beneficial effect on stress-induced gastrointestinal discomfort and may occur through alterations in gut microbiota composition and metabolism.