AbstractProbiotics are recognized to outcompete pathogenic bacteria by receptor-mediated colonizing and secreting functional metabolites which have direct antimicrobial activities towards pathogens and/or improving host’s gut health and immunity. We have constructed aLactobacillus casei(LC) probiotic strain, LC+mcra, by insertingmcra(myosin cross-reactive antigen) gene, which stimulates the conversion of conjugated linoleic acids. In this study, we evaluated the protective roles of LC+mcraagainst pathogenicSalmonella entericaserovar Typhimurium (ST) and enterohaemorrhagicE. coli(EHEC) infection in BALB/cJ mice. Through a series ofin vivoinvestigation, we observed that LC+mcracolonized efficiently in mice gut and competitively reduced the infection with ST and EHEC in various locations of small and large intestine, specifically cecum, jejunum, and ileum (p<0.05). The cecal microbiota in ST-challenged mice with LC+mcraprotection were positively modulated with higher relative abundances Firmicutes but lower Proteobacteria plus increased bacterial species diversity/richness based on 16S metagenomic sequencing. Based on cytokine gene expression analysis by qRT-PCR, mice pretreated with LC+mcrawere found with attenuated bacterial pathogen-induced gut inflammation. Furthermore, mice fed LC+mcradaily for one week could protect themselves from the impairments caused by enteric infections with ST or EHEC. These impairments include weight loss, negative hematological changes, intestinal histological alterations, and potential death. Thisin vivostudy suggests that daily consumption of novel conjugated linoleic acids over-producing probiotic might be efficient in improving gut intestinal microbiome composition and preventing/combating foodborne enteric bacterial infections with pathogenicSalmonellaand diarrheagenicE. coli.Author summaryNumerous bacteria colonize throughout the gastrointestinal tract and form a complex microbial ecosystem known as gut microbiota. A balanced microbial composition is crucial for maintaining proper gut health and host defense against pathogenic microbes. However, enteric bacterial infections could cause illness and even lead to death of host when foodborne pathogens likeSalmonellaand enterohaemorrhagicE. coli(EHEC) invade gut intestine and cause imbalance of gut microbiota. Beneficial microbes in gastrointestinal tract such asLactobacillusand their secreted bio-active metabolites, are potential bio-agents to improve gut immunity and outcompete bacterial pathogens. In this study, to evaluate roles of novelLactobacillusstrain LC+mcrawhich produce higher amount of a group of beneficial secondary metabolites called conjugated linoleic acids, we have shown that daily oral administration of this LC+mcrafor one-week in mice lead to higher proportion of beneficial bacterial colonization in different locations of intestine and a significant reduction of pathogenicSalmonellaand EHEC colonization. Furthermore, mice fed with LC+mcrarestore and modulateSalmonellainfection-induced negative impact on gut microbiota composition and protect themselves from various levels of physiological damage.
The Gut Microbiota Affects Host Pathophysiology as an Endocrine Organ: A Focus on Cardiovascular Disease