The Mechanism Study Of Lactic Acid Bacteria On Regulation Of Oxygen Concentration To Improve Animal Enteritis

Bacteria,viruses,chemicals,and environmental factors can cause intestinal inflammation,which seriously threatens the health of livestock and leads to enormous economic losses to the livestock and poultry industry.The specific pathogenesis of enteritis is still unclear,which mainly causing abdominal pain,diarrhea,bloody stools,etc.,and the treatment of enteritis is still difficult.At present,the main treatment of enteritis with antibiotics,but the long-term use and abuse of antibiotics lead to drug resistance.It is urgent to find a new treatment strategy.In recent years,probiotics have been widely studied,more and more evidence showed that supplement of probiotics can effectively alleviate intestinal inflammation.Probiotics can inhibit the growth of pathogenic microorganisms,increase the tight connection of epithelium,change intestinal permeability,and secrete antibacterial substances.The transportation and consumption of oxygen in the intestinal epithelium of animals can regulate the transport function of intestinal epithelium,promote the energy metabolism of intestines,and play an important role in maintaining the health of animal intestines.The previous research of this research group found that Lactobacillus reuteri(L.reuteri)D8 regulated STAT3 signaling pathway and influence the proliferation and differentiation of intestinal stem cells.In this study,we first explored the effect of L.reuteri on intestinal stem cells by regulating oxygen concentration in a mouse model,which laid a foundation for the study of the protective effect of Lactic acid bacteria on Salmonella typhimurium infected chicks.It was found that L.reuteri regulated intestinal oxygen concentration and promoted the proliferation of intestinal stem cells.However,it was found that L.reuteri had no significant protective effect against Salmonella typhimurium infection in chicks.One strain of Enterococcus faecium selected in this study could repair the damaged chicken intestinal mucosa to reduce the infection of Salmonella typhimurium.This article was mainly divided into the following two parts:1.Study on the regulation of oxygen concentration by lactic acid bacteria to promote the proliferation of intestinal stem cells.Previous studies in the laboratory have shown that L.reuteri D8 could colonize the intestinal mucosa of animal,activate laminaria propria lymphocytes to secrete IL-22,and induce STAT3 signaling pathway to promote intestinal stem cell regeneration,thereby improving intestinal inflammation.In this study,and C57BL/6 mice were orally administered with L.reuteri D8.By immunofluorescence,it was found that the treatment with L.reuteri D8 significantly increased the average fluorescence intensity of PCNA+ cells in the intestinal crypts compared with the blank control group,and the proliferation of intestinal stem cells was inhibited after treatment with hypoxia-inducible factor inhibitors.Furthermore,the expression of genes related to the Wnt/β-catenin pathway,such as Wnt3,Lgr5,Lrp5,c-Myc and Ki67,were detected by real-time quantitative PCR.The expression level of proliferation-related genes was significantly increased after L.reuteri D8 treatment,but the inhibitors inhibited the promotion of L.reuteri D8.We further tested the expression of hypoxia-inducible factor-related genes and target genes,such as HIF-1α,HIF-1β,HIF-2α,ITF and GLUT1,and the results indicated that L.reuteri D8 could induce intestinal hypoxia.The oxygen environment activates the expression of these hypoxia-inducible factors and downstream target genes,enhancing the intestinal mucosal barrier.The above results showed that under physiological conditions,L.reuteri D8 regulated the oxygen concentration and promote the proliferation of intestinal stem cells.2.Study on the mechanism of lactic acid bacteria regulating oxygen concentration to improve the enteritis caused by Salmonella typhimuriumTo explore the protective effect of lactic acid bacteria on chicks infected with Salmonella typhimurium,we fed chicks with L.reuteri D8 and the chicken-derived lactic acid bacteria selected in this study to explore their protection against Salmonella typhimurium.The 1-day-old white feather broilers were divided into sixteen groups,including the control group,the Salmonella typhimurium treated group,the Lactic acid bacteria treated groups(7 strains,including L.reuteri treated group),the Lactic acid bacteria and the Salmonella typhimurium treated simultaneously groups.The study found that after the chick was infected with Salmonella typhimurium,the liver showed obvious white necrosis foci,intestinal bleeding increased and intestinal villi were damaged.The weight of chicks infected with Salmonella typhimurium decreased significantly.L.reuteri could not maintain the weight of chicks after infection,but E.faecium YQH2 treatment could significantly improve the weight loss of chicks caused by Salmonella typhimurium infection.Therefore,the follow-up experiments further studied the protective effect of chicken-derived E.faecium YQH2 on chicks.The E.faecium YQH2 could alleviate liver and intestinal damage caused by Salmonella typhimurium in chicks,increase villus length and crypt depth.The level of enteric inflammatory factor TNF-α was increased when the chick was infected with Salmonella typhimurium,while E.faecium YQH2 protected the intestinal mucosa by reducing the level of TNF-α in the intestinal tissue.Detection of Salmonella colonization in feces,it was found that E.faecium YQH2 could significantly reduce the colonization of Salmonella,prevent it from invading the intestinal tract.Intestinal immunohistochemistry and the real-time quantitative PCR results indicated that the intestinal proliferation after Salmonella infection was inhibited,but E.faecium YQH2 could significantly augment the expression of intestinal proliferation genes(such as Wnt3,β-catenin and Lrp5),promote the proliferation of intestinal stem cells,accelerate the repair and regeneration of intestinal epithelium.After Salmonella typhimurium infection,the hypoxia-inducible factor of the intestine was activated,and at the same time,E.faecium YQH2 was able to significantly inhibit the expression of intestinal hypoxic inducible factor.The above results indicated that under the state of inflammation,E.faecium YQH2 could inhibit the expression of hypoxia-inducing factors and target genes,promote intestinal stem cell proliferation,and alleviate the intestinal damage caused by Salmonella typhimurium infection.