Salmonella enterica serovar Typhimurium (S. Typhimurium) has evolved mechanisms to evade the host’s nutritional immunity and thus promote bacterial growth by using the iron in the host. However, the detailed mechanisms of S. Typhimurium induce dysregulation of iron homeostasis and whether Lactobacillus johnsonii L531 can alleviate the iron metabolism disorder caused by S. Typhimurium has not been fully elucidated. Here, we show that S. Typhimurium activated the expression of iron regulatory protein 2 (IRP2), transferrin receptor 1, and divalent metal transporter protein 1 and suppressed the expression of iron exporter ferroportin, which resulted in iron overload and oxidative stress, inhibiting the key antioxidant proteins NF-E2-related factor 2, Heme Oxygenase-1, and Superoxide Dismutase in vitro and in vivo. L. johnsonii L531 pretreatment effectively reversed these phenomena. IRP2 knockdown inhibited iron overload and oxidative damage induced by S. Typhimurium in IPEC-J2 cells, while IRP2 overexpression promoted iron overload and oxidative damage caused by S. Typhimurium. Interestingly, the protective effect of L. johnsonii L531 on iron homeostasis and antioxidant function was blocked following IRP2 overexpression in Hela cells, demonstrating that L. johnsonii L531 attenuates disruption of iron homeostasis and consequent oxidative damage caused by S. Typhimurium via the IRP2 pathway, which contributes to the prevention of S. Typhimurium diarrhea in mice.

Salmonella enterica serovar Infantis (S. Infantis) is an intracellular bacterial pathogen. It is prevalent but resistant to antibiotics. Therefore, the therapeutic effect of antibiotics on Salmonella infection is limited. In this study, we used the piglet diarrhea model and the Caco2 cell model to explore the mechanism of probiotic Lactobacillus johnsonii L531 (L. johnsonii L531) against S. Infantis infection. L. johnsonii L531 attenuated S. Infantis-induced intestinal structural and cellular ultrastructural damage. The expression of NOD pathway-related proteins (NOD1/2, RIP2), autophagy-related key proteins (ATG16L1, IRGM), and endoplasmic reticulum (ER) stress markers (GRP78, IRE1) were increased after S. Infantis infection. Notably, L. johnsonii L531 pretreatment not only inhibited the activation of the above signaling pathways but also played an anti-S. Infantis infection role in accelerating autophagic degradation. However, RIP2 knockdown did not interfere with ER stress and the activation of autophagy induced by S. Infantis in Caco2 cells. Our data suggest that L. johnsonii L531 pretreatment alleviates the intestinal damage caused by S. Infantis by inhibiting NOD activation and regulating ER stress, as well as promoting autophagic degradation.