| Salmonella typhimurium is a kind of zoonosis and the main pathogen of salmonellosis in broilers.Antibiotics are commonly used for the prevention and treatment of Salmonellosis in clinical practice,but the non-standard use of antibiotics increases bacterial resistance,making the prevention and treatment of bacterial infections even more difficult.Therefore,there is an urgent need to develop a safe and environmentally friendly formulation to prevent the infection of Salmonella typhimurium.As a probiotic,there have been no reports on the use of Lentilactobacillus buchneri in preventing Salmonella typhimurium infection.Therefore,this study isolated,purified and screened a strain of Lentilactobacillus buchneri GXNN20210328-6(hereinafter referred to as GX0328-6)from the traditional fermented food pickled Chinese cabbage,and explored the biological characteristics and safety of GX0328-6,as well as the protective effect and mechanism of GX0328-6 on animals infected with Salmonella typhimurium SM022(hereinafter referred to as SM022).The specific research content and results are as follows:1.Biological characteristics and safety analysis of GX0328-6.Evaluated the biological characteristics and safety of GX0328-6 by testing its acid production capacity,tolerance,and safety.The results showed:(1)GX0328-6 was a Gram positive bacterium,and no mucus was found when it was stirred up.The colony morphology of this bacterium was milky white,round,with a smooth surface,neat edges,and ridges.(2)GX0328-6 inhibited the proliferation of Salmonella typhimurium,Escherichia coli,and Staphylococcus aureus.(3)GX0328-6 had the characteristics of safety,acid resistance,bile salt resistance,and high temperature resistance.2.Preventive and protective effects of GX0328-6 on SM022 infectedC57BL/6 mice.88 4-week-old female mice were randomly divided into 4groups(n=22):negative control group(Control,CON),GX0328-6 control group(Lentilactobacillus buchneri,LB),GX0328-6 prevention group(LB+Salmonella typhimurium SM022,LB+SM022),and positive group(Salmonella typhimurium SM022,SM022).CON and SM022 group mice were continuously gavaged with 0.2 m L of normal saline for 10 days,while LB and LB+SM022 group mice were continuously gavaged with 0.2 m L concentration of 1×10~8CFU/m L GX0328-6 bacterial suspension for 10 days,once a day.On the 11th day,0.2 m L concentration of 1×10~8CFU/m L SM022 bacterial suspension was gavaged once to mice in the SM022 and LB+SM022 groups.Detected the body weight,immune organ index,survival rate,expression levels of immunoglobulins and intestinal barrier related cytokines,liver and intestinal tissue morphology,and cecal microbiota of each group of mice to explore the preventive and protective effects of GX0328-6 on SM022 infected mice and its mechanism.The result showed:(1)GX0328-6 significantly alleviated symptoms such as mental depression,weight loss,liver injury,hepatosplenomegaly caused by SM022 in mice,and significantly reduced the load of SM022 in the liver(P<0.05),spleen(P<0.05),and cecum(P<0.0001)tissues of mice.(2)Compared with the SM022 group,the GX0328-6group significantly upregulated the expression of ZO-1 m RNA(P<0.01),Occludins m RNA(P<0.05),and Cludins-4 m RNA(P<0.05)in the mouse jejunum,significantly downregulated the expression of REGIII m RNA(P<0.05)and IL-6 m RNA(P<0.001),significantly increased the jejunal villus length(P<0.01)and the ratio of villus length to crypt depth(P<0.001),significantly reduced the jejunal crypt depth(P<0.001).Additionally,GX0328-6 significantly increased the relative abundance of beneficial bacteria(P<0.05),and significantly reduced the relative abundance of harmful bacteria(P<0.05)in the cecum of mice.3.The preventive and protective effect of GX0328-6 on sanhuang chicks infected with SM022.360 1-day-old chicks were randomly divided into4 groups in the experiment,with 6 replicates in each group and 15 chicks in each replicate.The bacterial suspension and feeding method used in the experiment were the same as those of mice.The dosage and concentration of GX0328-6 and SM022 bacterial suspension were 1 m L,with a concentration of 1 m L×109 CFU/m L,chicks start feeding on the first day.Detected the effects of GX0328-6 on the body weight,immune organ index,liver and jejunal tissue morphology,SM022 load in liver,spleen,and cecal tissues,as well as the microbiota in the cecum of chicks infected with SM022,in order to explore the preventive and protective effects of SM022 infection in chicks.The result showed:(1)GX0328-6 significantly alleviated the thymus atrophy(P<0.05),weight loss(P<0.05),liver and intestinal pathological damage caused by SM022 in chicks,significantly reduced the load of SM022 in liver(P<0.0001),spleen(P<0.05)and cecum(P<0.01)tissues in chicks.(2)Compared with the SM022 group,GX0328-6 group significantly increased the villus length,the ratio of villus length to crypt depth(P<0.001),significantly reduced crypt depth(P<0.001)in the jejunum of chicks,moreover,it significantly increased the relative abundance of beneficial bacteria such as Rhodobacterales(P<0.01)and Rombousia(P<0.05),significantly reduced the relative abundance of the harmful bacteria such as Desulfulomonadia(P<0.05)and PB19(P<0.05)in the cecum of chicks.In summary,this study isolated and screened a strain of Lentilactobacillus buchneri with acid resistance,bile salt resistance,high temperature resistance,and safety.Through exploring the preventive and protective effects of Salmonella typhimurium infection in C57BL/6 mice and sanhuang broiler chicks,it was found that GX0328-6 can effectively prevent Salmonella typhimurium infection by regulating the intestinal barrier.It is suggested that Lentilactobacillus buchneri GX0328-6 can be used as a candidate strain for probiotic preparations.This study can provide a theoretical basis for probiotics as feed additives. |
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