Effects Of Probiotics On Chickens' Resisitance To Escherichia Coli Infection And Genome Analysis

Pathogenic Escherichia coli?E.coli?is a common pathogenic bacteria with strong infectivity and drug resistance.It is easy to cause large-scale colibacillosis?Colibacillosis?and pose a great threat to the animal breeding industry.Intestinal microbes always affect the health of the body,and the use of probiotics usually can have a positive impact on animal health.Therefore,in the context of strict restrictions on the use of antibiotics,the use of probiotics to regulate the health of the body and resist bacterial infectious diseases has become a popular direction of applied research.The purpose of this study is to obtain useful probiotics with application value,and to explore the effects of probiotics on the resistance of chicks to E.coli infection,and provide a theoretical basis for the development of micro-ecological preparations.The details are as follows:?1?Through the Oxford Cup test of the supernatant of fermentation broth,the co-culture bacteriostasis test and Escherichia coli?XT-13?adhesion inhibition test,the in vitro antibacterial effects of three probiotics were preliminarily explored.The three bacteria were Lactobacillus plantarum ZN-3?ZN-3?,Lactobacillus rhamnosus QC?QC?and Clostridium butyricum HYCB?HYCB?.The results showed that the supernatant of each probiotic fermentation broth had obvious bacteriostatic effect,and the proliferation of Escherichia coli was significantly inhibited when co-cultured with these three probiotics.In addition,the equal proportion of the three mixed bacteria X could significantly reduce the adhesion rate of XT-13to DF-1 cells?Chicken embryo fibroblasts,DF-1?.That is,these three probiotic strains have a synergistic effect.?2?In order to explore the protective effect of probiotics on chickens infected with E.coli,and obtain the best probiotics or their combination,7-day-old SPF chickens were given ZN-3?3×10⁸CFU/m L?,QC?3×10⁸CFU/m L?,HYCB?3×10⁸CFU/m L?and equal proportion mixed bacteria X respectively for 30 days.The chickens were orally infected with Escherichia coli XT-13(2×10¹⁰ CFU/m L)once a day from the 26th to the 30th day,and the weight change and survival rate of chickens infected with XT-13 were recorded to evaluate the protective effect..The results showed that the mixed probiotics had better protection effect,and the weight gain effect of mixed probiotics was better than that of probiotics alone.According to the course of infection in the protection test,chickens were dissected on the 8th day after XT-13 infection,and the results were recorded,tissue sections were made and pathological changes were analyzed.At the same time,the difference of bacterial load in liver and intestine was detected by immunohistochemistry.The results showed that the mixed probiotic X can reduce the pathological damage of the organs of the chicks after infection with XT-13,and reduce bacterial load in liver and large intestine,which is of great significance to reduce the risk of systemic infection and mortality.?3?In order to further understand the effect of mixed probiotic X on the growth status and immune-related indicators of chicks infected with XT-13,this study measured and compared the weight and intestinal villi indicators of chicks after being fed X,and found that X increased the ratio of ileal villi length to crypt depth and the depth of large intestine glands,and the weight gain of chicks was obvious.At the same time,this study also detected the levels of IL-10?Interleukin-10?and IL-17?Interleukin-17?in serum and defensin?AvBD1?in the liver on days 4,8 and 14 after chicks were infected with XT-13,and the serum survival test of XT-13 was carried out using the serum on the 14th day to initially assess the immune level of the body.The results show that mixed probiotic X can regulate the level of serum IL-10 and IL-17 and the content of liver DEF-?1,and increase the level of serum sterilization,reducing the risk of morbidity and mortality of chicks.That is,mixed probiotic X can regulate the host's immune response,help the host resist infection and restore health.?4?In order to further evaluate the broad-spectrum protective effect of X on avian colibacillosis,the protective effect of X on chickens infected with clinical strain O78 serotype E.coli AV006 was also evaluated.The results showed that X increased the survival rate of chickens and had a good protective effect on O78 avian colibacillosis.It has a broad application prospect and is suitable for the development of probiotics.?5?In order to gain a deeper understanding of the characteristics and value of these three probiotics,this study performed second-generation sequencing and bioinformatics analysis on their genomes.The results show that,in general,the three probiotic bacteria have their own characteristics in terms of metabolic activity and production of antibacterial substances.Among them,it is worth noting that a variety of phytolactins are predicted in ZN-3,a series of enzyme systems with complete antioxidants?Carotenoids?,and the synthesis of vitamin B6and vitamin B12 and a variety of essential Nutrients such as amino acids;Hydrogen production,spore formation,CRISPR system and lasso peptide synthesis gene cluster are predicted in HYCB.These genomic features reveal the potential development value of probiotics in this study.