Fig 2: The main mechanism diagram of this study. L. johnsonii L531 reverses S. Typhimurium-induced iron metabolism disorder and oxidative stress via IRP2 pathway, thereby contributing to alleviating S. Typhimurium diarrhea.

Fig 3: S. Typhimurium promotes its growth and induces oxidative stress via the IRP2 pathway in IPEC-J2 cells. (A) The intracellular bacterial load. (B) Analysis of S. Typhimurium intracellular localization. Blue, DAPI. Green, S. Typhimurium. Scale bar, 10 μm. (C) ROS levels. Scale bar, 100 μm. (D) Western blot analysis of Nrf2 and HO-1. (E) The detection of mRNA expression levels on NQO1, SOD1, and GPX1. Values are expressed as the means ± SEM of 3 independent experiments. * p < 0.05, ** p < 0.01, *** p < 0.001.

Fig 4: L. johnsonii L531 ameliorates disturbance of iron metabolism and diarrhea induced by S. Typhimurium in vivo. (A) Experimental design. Viable cell count of intracellular S. Typhimurium in liver (B) and feces (C) was determined by plating (n = 6 mice, respectively). (D) The results of the dry/wet weight ratio of the feces. (E) Ileum and liver representative photomicrographs of sections stained with H&E. In the ileum, the green arrow indicates atrophy of ileal intestinal glands, red arrow indicates basement membrane mucosal oedema, and black arrow indicates intestinal glands detached from basement membrane. In the liver, the red arrow indicates disturbed hepatocyte arrangement, green arrow indicates inflammatory cell infiltration, and black arrow indicates hepatocyte degeneration and necrosis. Ileum (F), hepatic (G), and serum iron (H) levels (n = 6 mice, respectively). (I) Western blot analysis of IRP2, DMT1, TfR1, and FPN in ileum. Distribution of IRP2 in ileum (J) and liver (K) by immunofluorescence staining. IRP2: Red (Ileum), Green (Liver), Blue: DAPI. Scale bar, 100 μm. Values are expressed as the means ± SEM of 3 independent experiments. * p < 0.05, ** p < 0.01, *** p < 0.001.

Fig 5: L. johnsonii L531 suppresses the high expression of IRP2 and alleviates oxidative stress caused by S. Typhimurium. (A) Western blot analysis of IRP2. (B) Distribution of IRP2 (Red) and S. Typhimurium (Green) in IPEC-J2 cells by immunofluorescence staining. Blue: DAPI. Scale bar, 10 μm. (C) DCFH-DA staining to assess ROS. Scale bar, 100 μm. (D) Western blot analysis of Nrf2 and HO-1. (E) The NQO1, SOD1, and GPX1 mRNA expression levels. Values are expressed as the means ± SEM of 3 independent experiments. * p < 0.05, ** p < 0.01, *** p < 0.001.