Psychobiotic bacteria hold promise for modulating the gut-brain axis, particularly under stress-induced dysbiosis. In this study, nine psychobiotic formulations were evaluated using a novel simplified batch version (M-batches) of the Simulator of the Human Intestinal Microbial Ecosystem, including the mucosal compartment (M-SHIME®), inoculated with fecal samples from highly stressed donors. Several treatments, particularly those containing Heyndrickxia coagulans [ATB-BCS-042] with either Levilactobacillus (Lv.) brevis [THT-030-201] or Lactiplantibacillus plantarum [THT-030-702], led to significant increases in Bifidobacterium and Akkermansia muciniphila. Modulations in butyrate-producing taxa were observed with H. coagulans + Lactobacillus (L.) gasseri [THT-031-301] and Enterococcus faecium [ATB-EFM-030] + Lactobacillus helveticus [THT-031-102]. Combinations of H. coagulans with either Lv. brevis, L. gasseri, or Lactobacillus johnsonii [THT-032-401] facilitated lactobacilli colonization. Dopamine levels increased with E. faecium + Lacticaseibacillus (Lc.) paracasei [THT-031-901] and H. coagulans + L. johnsonii, whereas other metabolites, such as Short Chain Fatty Acids (SCFA) and ammonia, remained largely unchanged across treatments. Metabolic outputs also included aryl hydrocarbon receptor (AhR)-activating metabolites, with the strongest effect seen for H. coagulans + L. gasseri, suggesting involvement with stress-related host signaling pathways. Among all probiotics, cocktails containing H. coagulans with either Lv. brevis or L. gasseri produced the most consistent and multifaceted effects. These findings underscore psychobiotic formulations that enhance gut microbiota resilience and boost metabolites potentially influencing host pathways under stress. Using fecal microbiota from highly stressed donors offers a promising in vitro approach that better reflects stress-related gut ecosystems for translational microbiome-brain axis research.
