To investigate the metabolic characteristics of salmon muscle consumed raw under fluctuating temperature chilled conditions, differential metabolites in salmon samples stored for different periods (0, 4 and 9 days) at 4 or 10 ℃ were analyzed by ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS)-based metabolomics combined with multivariate statistical analysis. Results showed that the composition of metabolites was significantly different between fresh and stored salmon at each temperature (P < 0.05), and the difference was more obvious in samples stored at 10 ℃. By orthogonal partial least squares-discriminant analysis (OPLS-DA), 47 and 62 differential metabolites were identified between fresh salmon and samples stored at 4 and 10 ℃, respectively, including lipids and lipid-like compounds, amino acids and their derivatives, organic acids and their derivatives, nucleotides and their derivatives. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis and metabolic path mapping showed that the biosynthesis of amino acids was the important metabolic pathway for salmon samples stored at 4 ℃. L-Histidine and L-tryptophan were involved in more metabolic pathways and, therefore, could be used as metabolic markers for raw salmon stored at 4 ℃. Additionally, the energy metabolism pathway was the major metabolic pathway for salmon samples stored at 10 ℃, and L-histidine, pyruvate, linolenic acid and purine metabolites played important roles and thus could be used as metabolic markers for raw salmon stored at 10 ℃.

The protective effect of Bacillus subtilis JZXJ-7 (JZXJ-7) on Vibrio parahaemolyticus (Vp) infected mice was investigated. Totally 28 male C57BL/6J mice were randomly divided into four groups: a Vp infection model group (infected with the standard virulence strain ATCC33847), two JZXJ-7 intervention groups (administered at low (10⁶ CFU) and high (10⁸ CFU) doses by gavage), and a control group. The control and model groups were administered with an equal volume of normal saline. Disease activity index (DAI), Vp load in the intestine tract (including the ileum, cecum, and colon), colonic pathological alterations, colonic cytokine contents, oxidative stress resistance, and changes in intestinal microbial community composition were detected in all groups. The results showed that the protective effect of JZXJ-7 was better at the high dose than at the low dose. High-dose JZXJ-7 significantly reduced the DAI and intestinal Vp load in Vp infected mice, alleviated inflammatory cell infiltration and collagen deposition, and increased the number of intestinal epithelial goblet cells (P < 0.05). Moreover, high-dose JZXJ-7 significantly inhibited cytokine-mediated inflammation, increased antioxidant enzyme activities and enhanced intestinal permeability. Furthermore, JZXJ-7 significantly increased (P < 0.05) intestinal microbial diversity, partially reversing intestinal flora disturbance, enriching Akkermansia, Bifidobacterium, Clostridium and other beneficial bacteria, and thus resulting in the restoration of intestinal microecological homeostasis. In summary, JZXJ-7 can effectively alleviate colonic pathological damage in Vp infected mice and maintain intestinal functions, and the underlying mechanism may be related to its regulatory effect on the intestinal microbiota.