Postbiotic S-layer Protein 2 from Human Lactobacillus crispatus 2029 Strain is a Natural Perforator of the Outer Membrane of Multi-drug Resistant Salmonella Enteritidis and a Protector of Intestinal Homeostasis in Humans and Animals

Salmonella Enteritidis (SE) colonizes the intestines of chickens and pigs, which leads to food contamination and increases the risk of pathogen transmission to humans. Multi-drug resistant (MDR) strains of SE are particularly dangerous. Surface-layer proteins (Slps) secreted by lactobacilli have various beneficial effects. However, the importance of these postbiotics in protecting against MDR SE and maintaining intestinal homeostasis has not been well studied. In this work, we investigated the role of Slp2 of human vaginal Lactobacillus crispatus 2029 (LC2029) strain in safeguarding human and animal intestinal epithelial monolayers from MDR SE and for maintaining intestinal homeostasis. It was shown for the first time that Slp2 inhibited intestinal adhesive and invasive activity of MDR SE and perforated the outer membrane of this pathogen, resulting in the leakage of ATP from the cell. The use of qRT-PCR has shown that Slp2 inhibits the expression of SE virulence genes required for colonization of enterocytes and the salmonellosis development. Slp2 suppressed SE-induced synthesis of proinflammatory cytokines (IL-8, TNF-α, Il-1β), the expression of TLR4 and enhanced synthesis of intestinal homeostatic factor - intestinal alkaline phosphatase (IAP) in enterocytes. As a protector, Slp2 prevented the development of SE-induced intestinal barrier dysfunction in monolayers of human, porcine and chicken enterocytes. The results of this study make a significant contribution to understanding the mechanisms of Slp2 action as a natural protector of human, porcine and chicken intestinal homeostasis and increase the effectiveness of the international concept “One Health” implementation.