Lactiplantibacillus plantarum Postbiotics Suppress Salmonella Infection via Modulating Bacterial Pathogenicity, Autophagy and Inflammasome in Mice

SIMPLE SUMMARY: Salmonella infection is an urgent problem in animal husbandry, which causes salmonellosis in livestock and poses threats to human health through contaminated livestock products. As an alternative to antibiotics, probiotics play an important role in maintaining animal health. However, some probiotics, such as lactic acid bacteria, have limitations in storage and hostile environments. In this context, exploring the bacterial components or metabolites of probiotics has gradually drawn more research interest, and these are termed “postbiotics”. This study investigated the antibacterial effect of Lactiplantibacillus plantarum (LP) postbiotics and compared the effects to the live bacteria on intestinal health and autoimmunity in mice challenged with Salmonella. The results showed LP culture supernatant directly inhibited Salmonella growth and pathogenicity. LP postbiotics (the heat-killed bacteria and metabolites) showed similar or even superior effects to the active probiotic against Salmonella in mice. Furthermore, we found that LP postbiotics alleviated Salmonella infection via modulating bacterial pathogenicity, autophagy and inflammatory response. These results provide a theoretical basis for the protection of LP postbiotics against Salmonella and help to further explore its role in animal husbandry. ABSTRACT: Our study aimed to explore the effects of postbiotics on protecting against Salmonella infection in mice and clarify the underlying mechanisms. Eighty 5-week-old C57BL/6 mice were gavaged daily with Lactiplantibacillus plantarum (LP)-derived postbiotics (heat-killed bacteria, LPB(inactive); culture supernatant, LPC) or the active bacteria (LPB(active)), and gavaged with Salmonella enterica Typhimurium (ST). The Turbidimetry test and agar diffusion assay indicated that LPC directly inhibited Salmonella growth. Real-time PCR and biofilm inhibition assay showed that LPC had a strong ability in suppressing Salmonella pathogenicity by reducing virulence genes (SopE, SopB, InvA, InvF, SipB, HilA, SipA and SopD2), pili genes (FilF, SefA, LpfA, FimF), flagellum genes (FlhD, FliC, FliD) and biofilm formation. LP postbiotics were more effective than LP on attenuating ST-induced intestinal damage in mice, as indicated by increasing villus/crypt ratio and increasing the expression levels of tight junction proteins (Occludin and Claudin-1). Elisa assay showed that LP postbiotics significantly reduced ST-induced inflammation by regulating the levels of inflammatory cytokines (the increased IL-4 and IL-10 and the decreased TNF-α) in serum and ileum (p < 0.05). Furthermore, LP postbiotics inhibited the activation of NOD-like receptor thermal protein domain-associated protein 3 (NLRP3) inflammasome by decreasing the protein expression of NLRP3 and Caspase-1, and the gene expression of Caspase-1, IL-1β and IL-18. Meanwhile, both LPC and LPB observably activated autophagy under ST infection, as indicated by the up-regulated expression of LC3 and Beclin1 and the downregulated p62 level (p < 0.05). Finally, we found that LP postbiotics could trigger an AMP-activated protein kinase (AMPK) signaling pathway to induce autophagy. In summary, Lactiplantibacillus plantarum-derived postbiotics alleviated Salmonella infection via modulating bacterial pathogenicity, autophagy and NLRP3 inflammasome in mice. Our results confirmed the effectiveness of postbiotics agents in the control of Salmonella infection.