Postbiotics are the inactive bacteria and/or metabolites of beneficial microbes which have been recently found to be as effective as their live probiotic. This study aimed to evaluate the benefits of Lactobacillus plantarum (LP)-derived postbiotics on ameliorating Salmonella-induced neurological dysfunctions. Mice were pretreated with LP postbiotics (heat-killed bacteria or the metabolites) or active bacteria, and then challenged with Salmonella enterica Typhimurium (ST). Results showed that LP postbiotics, particularly the metabolites, effectively prevented ST infection in mice, as evidenced by the inhibited weight loss, bacterial translocation, and tissue damages. The LP postbiotics markedly suppressed brain injuries and neuroinflammation (the decreased interleukin (IL)-1β and IL-6, and the increased IL-4 and IL-10). Behavior tests indicated that LP postbiotics, especially the metabolites, protected mice from ST-induced anxiety and depressive-like behaviors and cognitive impairment. A significant modulation of neuroactive molecules (5-hydroxytryptamine, gamma-aminobutyric acid, brain-derived neurotrophic factor, dopamine, acetylcholine, and neuropeptide Y) was also found by LP postbiotic pretreatment. Microbiome analysis revealed that LP postbiotics optimized the cecal microbial composition by increasing Helicobacter, Lactobacillus and Dubosiella, and decreasing Mucispirillum, norank_f_Oscillospiraceae, and Eubacterium_siraeum_group. Moreover, LP postbiotics inhibited the reduction of short-chain fatty acids caused by ST infection. Pearson's correlation assays further confirmed the strong relationship of LP postbiotics-mediated benefits and gut microbiota. This study highlights the effectiveness of postbiotics and provide a promising strategy for preventing infection-induced brain disorders by targeting gut–brain axis.

We previously found that Lactobacillus plantarum (LP)‐derived postbiotics protected animals against Salmonella infection, but the molecular mechanism remains obscure. This study clarified the mechanisms from the perspective of autophagy. Intestinal porcine epithelial cells (IPEC‐J2) were pretreated with LP‐derived postbiotics (the culture supernatant, LPC; or heat‐killed bacteria, LPB), and then challenged with Salmonella enterica Typhimurium (ST). Results showed that LP postbiotics markedly triggered autophagy under ST infection, as indicated by the increased LC3 and Beclin1 and the decreased p62 levels. Meanwhile, LP postbiotics (particularly LPC) exhibited a strong capacity of inhibiting ST adhesion, invasion and replication. Pretreatment with the autophagy inhibitor 3‐methyladenine (3‐MA) led to a significant decrease of autophagy and the aggravated infection, indicating the importance of autophagy in LP postbiotics‐mediated Salmonella elimination. LP postbiotics (especially LPB) significantly suppressed ST‐induced inflammation by modulating inflammatory cytokines (the increased interleukin (IL)‐4 and IL‐10, and decreased tumor necrosis factor‐α (TNF), IL‐1β, IL‐6 and IL‐18). Furthermore, LP postbiotics inhibited NOD‐like receptor protein 3 (NLRP3) inflammasome activation, as evidenced by the decreased levels of NLRP3, Caspase‐1 and apoptosis‐associated speck‐like protein containing a caspase recruitment domain (ASC). Deficits in autophagy resulted in an increase of inflammatory response and inflammasome activation. Finally, we found that both LPC and LPB triggered AMP‐activated protein kinase (AMPK) signaling pathway to induce autophagy, and this was further confirmed by AMPK RNA interference. The intracellular infection and NLRP3 inflammasome were aggravated after AMPK knockdown. In summary, LP postbiotics trigger AMPK‐mediated autophagy to suppress Salmonella intracellular infection and NLRP3 inflammasome in IPEC‐J2 cells. Our findings highlight the effectiveness of postbiotics, and provide a new strategy for preventing Salmonella infection.