Enterococcus faecium WEFA23 was previously found effectively against adherence and colonization of Listeria monocytogenes CMCC54007, which might be closely related to its surface layer protein (SLP). In this study, the protective of SLP of E. faecium WEFA23 against infection of L. monocytogenes CMCC54007 was systemically investigated. In vitro assay showed that SLP actively inhibited L. monocytogenes internalization into Caco-2 cell line, with decreasing mRNA level of pro-inflammation cytokines and virulence factors and restoring destroyed intestinal barrier. In vivo assay through excluding SLP of E. faecium WEFA23 by 5 M LiCl represented that SLP increased body weight, reduced mortality and cell counts of L. monocytogenes CMCC54007 in tissues of mice. Further researches showed that SLP protected against L. monocytogenes CMCC54007 infection by modulation of intestinal permeability and immunity, namely, it decreased fluorescein isothiocyanate (FITC)-Dextran in serum, ameliorated destroyed colon structure, and increased number of goblet cells and protein level of TJ protein (Claudin-1, Occludin, and ZO-1) in colon. For immunity, SLP decreased number of CD4+ and CD8+ T cells in liver, mRNA level, and content of pro-inflammatory factors IL-6, IL-1β, IFN-γ ,TNF-α, and NO, and restored the structure of liver and spleen. Key Points•SLP of E. faecium inhibited L. monocytogenes internalization and colonization•SLP of E. faecium ameliorated host intestinal barrier dysfunction•SLP of E. faecium decreased pro-inflammatory cytokines and cells.
Keywords: E. faecium WEFA23; Internalization; Intestinal barrier and immunity; L. monocytogenes CMCC54007; Surface layer protein.