肠道共生微生物与病原菌的相互作用是分子微生态学的研究热点与难点。作为首批婴幼儿肠道定植菌，肠球菌的益生/致病两重性对机体的微生态环境构建、免疫系统发育成熟起着特别关键作用。益生肠球菌与病原菌竞争、黏附肠道上皮细胞，行使益生功能，国内外研究颇少。前期工作中，分离获得一株婴儿源屎肠球菌WEFA23，其无毒力基因和表型，能定植肠道且能降低人体血清胆固醇，初步发现其表面蛋白E5能竞争抑制单核增生李斯特菌的菌体黏附，其作用机制亟待阐明。本项目拟采用生物信息学分析和基因敲除技术，获得屎肠球菌WEFA23的表面蛋白缺失突变株，在细胞水平上研究黏附蛋白定位、野生株和突变株拮抗单增李斯特菌的定植及毒素表达，对两者在小鼠体内对致病菌的拮抗和肠道免疫力进行探究。预期成果将发为有效利用益生肠球菌防控致病菌感染，提供实验基础。

The interaction between symbiotic microorganisms and pathogenic bacteria is a hotspot but difficulty point for studying in molecular microecology. As the first batch of infant intestinal colonization, the probiotic or pathogenic properties of Enterococcus is one of the critical factors for the balance of host flora system and development of immune system for infants. There are quite fewer studies on the competition for adhesion site of probiotic Enterococcus to intestinal epithelial cells. In our previous work, we isolated a strain of Enterococcus faecium WEFA23 from baby infants and proved it to have none virulence genes and phenotypes, it can colonize intestinal tract and reduce serum cholesterol. Remarkably, its surface protein E5 can inhibit the adhesion of Listeria monocytogenes, however, its mechanism is not clarified. This project intends to adopt bioinformatics analysis and gene knockout technology to obtain a mutant strain of E5 from the wild strain of Enterococcus faecium WEFA23, the wild and mutant strains as well as E5 surface protein were compared for the effect on the adhesion of Listeria monocytogenes, with the aim to disclose the mechanism of E5 against the pathogen or its toxins, also to ascertain the potential immunity enhancement in mice. The expected results will be meaningful for providing experimental basis for the effective use of probiotic bacteria in infection prevention and control of food-borne pathogens.