The Preventive Effect Of N-3 Polyunsaturated Fatty Acids On Salmonella Infection And The Mechanism

Salmonella is one of the most common food-borne pathogens.It is widely found in feces,soil,contaminated water and food.It can cause infections in animals and human,and cause symptoms such as typhoid,gastroenteritis,sepsis and even death.Salmonella causes enormous economic losses to the livestock industry each year and pose threat to public health and food safety.The preventive measures are mainly used to control Salmonella infection,while antibiotics are commonly applied in clinical treatment.n-3 polyunsaturated fatty acids have anti-inflammatory function,which could alleviate chronic inflammation such as atherosclerosis,cardiovascular disease,diabetes and arthritis.n-3 polyunsaturated fatty acids can also alleviate diseases caused by certain bacterial infections.However,there is no report on the prevention of Salmonella infection by n-3 polyunsaturated fatty acids.In this experiment,the mice model was used to investigate the preventive effect of n-3 polyunsaturated fatty acids(EPA and DHA)on Salmonella infection and its mechanism from various angles.This study established the foundation for the usage of n-3 polyunsaturated fatty acids in preventing and controlling Salmonella infection.The main results of this study are as follow:1.n-3 polyunsaturated fatty acids were effective in preventing Salmonella infection.The mice survival rate test proved that n-3 polyunsaturated fatty acids could increase the survival rate.Further experiments showed that n-3 polyunsaturated fatty acids could relieve colon,liver tissue lesions and splenomegaly caused by Salmonella infection.2.n-3 polyunsaturated fatty acids had no direct inhibitory effect on Salmonella in vitro.It was found that n-3 polyunsaturated fatty acids did not directly inhibit the growth of Salmonella in the medium containing different concentrations of fatty acids.After co-culture with HT-29 cells,the expression of Salmonella virulence genes was detected by PCR.The results showed that n-3 polyunsaturated fatty acids could not inhibit the expression of related virulence genes during the invasion.3.n-3 polyunsaturated fatty acids could play a role in regulating immune function.Real-time PCR result showed that n-3 polyunsaturated fatty acids could down-regulate the expression of IL-6 gene in mice liver.ELISA result showed n-3 polyunsaturated fatty acids could reduce the levels of pro-inflammatory factors IL-1? and IL-6 in serum while maintaining the anti-inflammatory factor IL-10 level.Meanwhile,by co-culturing Raw 264.7 cells and Salmonella,it was found that EPA and DHA could regulate the phagocytic function of macrophages.n-3 polyunsaturated fatty acids were effective in preventing Salmonella infection by regulating cytokines and immune cells and alleviate excessive inflammatory response after infection.4.n-3 polyunsaturated fatty acids could increase fecal short-chain fatty acid concentration.By measuring the short-chain fatty acid content by GC-MS,it was found that n-3 polyunsaturated fatty acids could significantly increase the total concentration of short-chain fatty acids,especially acetic acid and propionic acid in feces.Short-chain fatty acids have antibacterial ability.n-3 polyunsaturated fatty acids prevented Salmonella infection by altering the levels of short-chain fatty acids profile.5.n-3 polyunsaturated fatty acids could alter intestinal microbiota.By sequencing and analyzing the fecal microbiota,intestinal microbiota was changed after 7-day dietary supplementation with n-3 polyunsaturated fatty acids and the relative aboundence of Bifidobacterium,Bacteroides,Akkermansia were increased.n-3 polyunsaturated fatty acids affected short-chain fatty acid concentration by altering the intestinal microbiota,and intestinal microbiota may participate in immune regulation.