Study On Different Disease Resistance Ability In Various Chinese And Egyptian Representative Chicken Breeds

Globally,foodborne diseases are receiving increasing attention.Salmonellosis is one of the most common foodborne diseases worldwide,accounting for around 93.8 million foodborne illnesses and155,000 deaths per year.As a foodborne disease,Salmonella Typhimurium（ST）causes huge economic losses to the poultry industry and seriously threatens human public health.Poultry are considered to be important sources and carriers of the disease.ST also tends to be highly resistant to multiple antimicrobials,which has the potential to complicate the treatment of animal and human disease.An improved understanding of host immunological resistance and response mechanisms in different chicken breeds should be a top priority.The synbiotic analyzed in this study contained four probiotic bacterial strains（Lactobacillus reuteri,Enterococcus faecium,Bifidobacterium animalis,and Pediococcus acidilactici）and a prebiotic fructooligosaccharide,to raise the intestinal immunity of birds to face Salmonella infection.The objectives of the research described in this thesis were:（1）To identify the genes that were differentially expressed following infection of chickens with Salmonella Typhimurium in different chicken breeds[Beijing You（BY）and Cobb]using RNA sequencing;（2）Comparing the disease resistant ability of Egyptian local and commercial chicken breeds in response to ST challenge.（3）The role of Synbiotic（probiotic+prebiotic）in ST resistance of different chicken breeds（Fayoumi and Cobb）.To achieve these objectives,the research strategy involved construction of an improved disease model,transcriptome screening,identification of resistance genes and pathways and,evaluating the effect of synbiotic addition,by dietary supplementation on ST resistance.Firstly,the birds were orally challenged at 5 day of age by 2.4x10¹² cfu/ml ST.We found that differentially expressed m RNAs,as well as signaling pathways were investigated in BY chickens（BY,ST challenged-slight clinical symptoms and liver loads<10⁴ cfu ST）,Cobb（Cobb,ST challenged liver loads>10⁵ cfu ST）using the splenic and cecal tonsils transcriptome.A total of 775 significant differentially expressed genes（DEGs）in spleen and 456 DEGs in cecal tonsils were identified in comparisons among the BY and Cobb birds.The DEGs involved in the immune response pathways,were identified including the intestinal immune network for Ig A production,the cytokine–receptor interaction,Toll-like receptor signaling pathway,natural killer cell-mediated cytotoxicity,phagosome,antigen processing and presentation and NOD-like receptor signaling pathway.In addition,enriched pathways related to the interaction and adhesion between intestinal microorganisms and epithelial cells,including focal adhesion,regulation of actin cytoskeleton,cell adhesion molecules（CAMs）and the extracellular matrix（ECM）–receptor interaction,PI3K-Akt signaling pathway,Jak-STAT signaling pathway and salivary secretion.There was evidence of cross-talk among these pathways,perhaps contributing to susceptibility to Salmonella infection.From this finding we confirmed that BY chickens more resistance to ST infection compared to Cobb chickens.To investigate whether provision of synbiotic altered the expression of immune and inflammatory genes during Salmonella infection,the synbiotic added to the diet of Fayoumi and Cobb chicks with 1g/kg from the first day then orally challenged at 21 day of age by 3x10¹² cfu/ml ST.We noted that dietary synbiotic reduced the bacterial burden in liver and cecum,increased Lysozyme and decrease IL-6 level in plasma,and decreased relative abundance of IL-1β,TNF-α,IL-6,IL-8 and TLR4 transcripts in liver,spleen and cecal tonsils.The same trend with comparing Fayoumi to Cobb chickens.Taken together,these findings proved that synbiotic have a positive effect in ST infection by reduce production of the pro-inflammatory cytokines,and Fayoumi chickens was more resistance to ST compared Cobb chickens.In conclusion,the local chicken breeds Fayoumi and BY are more resistant to ST infection than commercial breeds（Cobb）.The supplementation of synbiotic in the chicken diet from the first day could modulate the host immune response and decrease the effect of Salmonella infection in chickens.This research with chicks has systematically exposed novel information on the immune mechanism of the host in providing some protection against Salmonella by use of a high-throughput sequencing combined with an improved experimental design strategy.Several important signaling pathways have been identified as intestinal immune network for Ig A production,Toll-like receptor signaling pathway,Natural killer cell-mediated cytotoxicity,Antigen processing and presentation,NOD-like receptor signaling pathway and Jak-STAT signaling pathway.These mechanistic findings will help facilitate the understanding of resistance and susceptibility to Salmonella infection in different chicken breeds of the host immune response,they will provide new approaches for developing strategies for Salmonella prevention and treatment,and they may aid in enhancing innate resistance using genetic selection and breeding with local chicken breeds.