Immunogenetic Response And Gut Microbiota Diversity In Jining Bairi Chicken Following Salmonella Enteritidis Infection

Salmonella enteritidis(SE),which blongs to gram-negative species,is a common zoonotic pathogens.It can cause huge economic losses to poultry industry by causing the incidence of death in poultry.It can even infect humans,causing human’s food poisoning,so that it is one of the important pathogens which impact human health.In this study,Chinese indigenous chicken breeds’ characteristic of disease resistance was set as a starting point,Salmonella enteritidis negative Jining Bairi chickens were randomly divided into two groups.The test group were perfused orally with Salmonella enteritidis,while the control group received the same amount of sterile PBS.Immune organs index were measured at 1,3,7,14,21,28 and 35 days post infection respectively.The structure of jejunal villi of Jining Bairi chicken were measured for a histological observation using paraffin section and H.E.staining methods,and the impact of Salmonella enteritidis on intestinal mucosal villous structures were compared by microscopic image analysis techniques and statistical methods.The changes of TLR2 and TLR4 gene expression of cecum tissue were detected using quantitative PCR and the serum cytokine levels were detected using ELISA.To get a better understanding of the impact of Salmonella enteritidis to the composition and structure of intestinal microflora,the DNA of cecal contents of both control group and test group were send to company for 16 S DNA sequencing.The results are as follows:(1)After Salmonella enteritidis infection,the weight gain of test group were higher than that of control group at different time points,but the weight and the immune organ index were not different significantly.7 time points after infection,the increase extent of villus length of the control group were greater than test group,and the length of villi of test group at the first day post infection was significantly lower than that of control group(P<0.05).The ratio ofvillus length and crypt depth(V/C)of the control group were higher than that of test group post infection,showing that Salmonella enteritidis infection reduces the digestion and absorption capacity of Jining Bairi chickens.(2)The result of quantitative PCR showed that the expression of TLR2 in cecum at 3 and21 days post infection was significantly different(P<0.01),with the expression levels of test group were 2.0 times(3DPI)and 1.5 times(21DPI)higher,respectively.At 3 days post infection,the expression of TLR4 of the test group was 1.8 times higher than that in control group,and the difference was significantly(P <0.01),the expression level of TLR4 of the two groups were significantly different(P <0.05)at 21 days post infection.(3)The results of 16 Sr DNA sequencing showed that the operational taxonomic units(OTUs)of test group was decreased significantly,indicating a significant reduction of cecal microbial species diversity in the test group.At the level of the phylum,cecal contents seven phylums,in which the abundance of Tenericutes,Proteobacteria and Bacteroidetes were reduced while the abundance of Firmicutes and Actinobacteria were increased due to the Salmonella enteritidis infection.At the early days after infection,the dominant bacteria were Proteobacteria and Firmicutes while at the late days became Bacteroides and Firmicutes.The result of principal component analysis(PCA)of diversity of cecal contents showed that there has significantly different between the two groups at 14 days post infection(P<0.05),illustrating that the infection SE changed the community structure and composition of cecal microbial.In summary,the infection of Salmonella enteritidis reduced the digestion and absorption capacity of Jining Bairi chickens’ jejunum,and it cut down the microorganisms species of cecal contents while altered the structure and composition of the intestinal microbial community.Furthermore,the infection of Salmonella enteritidis also affect the expression of immune genes in host.This study provide a scientific basis of the control mechanism and the genetic resistance mechanism of local chicken breeds to Salmonella enteritidis infection,and laid a theoretical basis to disease resistance breeding.