The Pathogenic Mechanism Of Salmonella Enteritidis And The Effect Of Clostridium Butyricum Against Salmonella Enteritidis Infection

Salmonella is a major global food-borne pathogen.It mainly infected producing animals e.g.chicken and swine,and the Salmonella were probably infecting human being via food chain from food producing animals and have threatened the public security yet.Poultry have been recognized as an important reservoir for Salmonella.The most frequently isolated serovar from chickens is S.enteritidis.In recent years,during to the antibacterial is widely used,the problem of drug-resistance strains increased,and it forced us to consideration of sustainable alternatives to antibiotics to fight against infections.Clostridium butyricum is concerned with its wide spectrum antimicrobial activity,not easily resistance to drug and extensive biological function.Preliminary study demonstrated that C.butyricum could improve animal production performance,enhance immune function,and reduce the colonization of the pathogenic bacteria,therefore weaken the inflammatory response,However,the protection mechanism of C.butyricum against Salmonella in chicks remains to be elucidated.On the basis of understanding the resistance characteristics of Salmonell,we performed to understand the pathogenic mechanism of Salmonella and the effect of Clostridium butyricum against Salmonella enteritidis infection.The following research was conducted.1.The antimicrobial resistance of Salmonella from animalsThe aim of the present study was to investigate the epidemiology of Salmonella from animals.A total of 13,00 samples were collected from eight areas of Shandong province between March 2015 and July 2016.Then,these samples were submitted to isolate the Salmonella,and these isolated bacteria were further identified.After then,the serotypes,sensitivities to 14 kinds of antibiotics,diversity and ST types of these Salmonella were analyzed by plate agglutination test,K-B method,and MLST analysises,respectively.In the present study,181 independent Salmonellas were isolated in total.The plate agglutination test classified them into seven serotypes,and the Indiana（40.3%）and Enteritidis（30.4%）were the prevalent.The results of the drug sensitive tests showed that these Salmonellas were resistance to the Ampicillin most,accounting for 70.0%.The multi-drug resistance rate was accounted for 69.6%.Class 1 integrons were detected in 21.0%of these isolates and most of them contained gene cassettes drfA17-aadA5（1.6 Kb）.Most of these isolates carried bla_TEM-1（98.3%）.Moreover,they were divided into nine ST types,The ST17 involved the highest isolation rate at 40.3%.2.The pathogenesis of Salmonella and the protection mechanism of Clostridium butyricum against Salmonella enteritidis infection in broilersThis study was designed to evaluate the pathogenesis of Salmonella and the protection mechanism of oral administration of Clostridium butyricum（C.butyricum）aganist Salmonella enteritidis（SE）colonization in broilers.In the current study,180 one-day-old healthy Arbor Acres（AA）broilers were meanly grouped into three,with three replicates of 20birds each.An negative control group（NC）was fed basal diet without SE challenge and a positive control group（PC）was fed the basal diet and challenged with SE（10⁶CFU/0.2 mL）.An experimental group（EG）was fed the basal diet,orally administered with C.butyricum（10⁶CFU/mL）and challenged with SE（10⁶CFU/0.2 mL）.The results showed that compared to the PC group,the SE loads in livers,spleens and cecal contents of chickens in EG group were significantly reduced（P<0.05）except in spleens at the 2 day post-infection;the production of interferon（IFN）-γ,interleukin（IL）-1β,（IL）-8,and tumor necrosis factor（TNF）-αin the livers,spleens,and cecal tissues of chickens in EG group were decreased to different extents.The results of quantitative real-time polymerase chain reaction（Q-PCR）further revealed that the inflammation of chickens in EG group was alleviated by C.butyricum via down-regulating TLR4,MyD88 and NF-κB-dependent pathways.Collectively,these findings indicated that oral administration of C.butyricum could be a suitable alternative for preventing SE infection in broilers.3.The mechanism of Clostridium butyricum on intestinal inflammation and intestinal epithelial barrier function by specific-pathogen-free chicken of Salmonella infectionThis study was aimed to investigate the effects of Clostridium butyricum（C.butyricum）on immunity and intestinal epithelial barrier function at intestinal mucosal level,by using Salmonella enteritidis（S.enteritidis）-infected specific-pathogen-free（SPF）chickens and intestinal epithelial cells.The results showed that C.butyricum could increase in the secretory-IgA in serum,and decreased cytokines（IFN-γ,IL-1β,IL-8 and TNF-α）via TLR4-,MyD88-,and NF-κB-dependent pathways in serum,intestinal tissues and intestinal epithelial cells.Additionally,C.butyricum could attenuate bacteria-induced intestinal damage and increase the expression level of muc-2 and ZO-1 in the intestine and intestinal epithelial cells.C.butyricum increased the percentage of CD4⁺/CD8⁺in peripheral blood lymphocytes cells of S.enteritidis-infected chicken.Furthermore,C.butyricum altered the intestinal microbial composition,increased the the diversity of the bacterial communities and promoted the immunity function in the cecum of Salmonella-infected chicken.In addition,the number of differential proteins caused by C.butyricum was lower than that of Salmonella infection and up-regulated the expression of related genes of drug metabolism pathway.In conclusion,this study provides basic data and guidance for applying C.butyricum in the prevention and treatment for Salmonella infection and reducing the use of antibiotics in animals.