| Salmonella typhimurium is a major foodborne enteric pathogen capable of causing different diseases,from self-limiting gastroenteritis to systemic infections,and infecting many different hosts,including humans,livestock and poultry.It has caused serious economic losses to livestock and poultry industry and posed a great threat to public health security.Use of antibiotics is an effective means to treat infection of Salmonellosis typhimurium,but with the increasing problem of antibiotic drug residues and drug resistance,probiotics as one of the many alternatives to antibiotics have attracted wide attention.However,in many current studies,the probiotics developed often used in the prevention and treatment of infection of Salmonella enteritidis,while the research reports on the development of effective probiotics for prevention and treatment of Salmonella typhimurium infection are relatively few.Therefore,it is increasingly important to find high-quality probiotics that can effectively prevent and control infection of Salmonella typhimurium and apply them in clinical production practice.Therefore,in this paper,the biological characteristics and in vitro antibacterial effects of Lactobacillus plantarum GX20200417-1,as well as the protective effects on chicks infected with Salmonella typhimurium and the effects on immunity and intestinal health of chicks were studied.This provides a theoretical basis for the development of probiotic candidate strains and their application in production as feed additives and antibiotic substitutes.The main research contents and results as follows:1.Study on the biological properties and in vitro antibacterial activity of Lactobacillus plantarum GX20200417-1.In this study,a candidate strain of Lactobacillus plantarum GX20200417-1,which was preliminarily screened in laboratory,was studied on its biological characteristics and in vitro bacteriostasis.The results showed that Lactobacillus plantarum GX20200417-1 could tolerate pH2.0 and 0.3%bile salt conditions,and had at least 1×104 CFU/mL viable bacteria count in artificial gastric and intestinal fluids.Lactobacillus plantarum GX20200417-1 had obvious inhibitory effect on Escherichia coli,Salmonella and Staphylococcus aureus.It had degradation effect on gibberellin and aflatoxin,but had no degradation effect on vomitoxin.After administration of Lactobacillus plantarum GX20200417-1,the mice were safe,which proved that the probiotics had no side effects on mice.The results showed that the Lactobacillus plantarum GX20200417-1 had good biological characteristics and bacteriostatic effect in vitro.2.Effect of Lactobacillus plantarum GX20200417-1 on chicks’ resistance to Salmonella infection.A total of 375 healthy 1-day-old yellow-feathered broilers were randomly divided into 5 groups:LP group,LP+Sty group,S+Sty group,Sty group and Control group with 5 replicates per group and 15 chicks per replicate.During 1 to 7 days,Group LP was fed the basal diet with Lactobacillus plantarum GX20200417-1(1.5×109 CFU/each)in the drinking water,and PBS was administered for 8 to 9 days.LP+Sty group:During 1 to 7 days,Lactobacillus plantarum GX20200417-1(1.5×109 CFU/each)live bacteria solution was added to the drinking water,and each chick was given 1mL of 1.5×109 CFU/mL Salmonella typhimurium on 8 to 9 days.S+Sty group二 During 1 to 7 days of experiment,1.5 ×109 CFU/each of commercial complex probiotic liquid was added to the drinking water,and each chick was given 1mL of Salmonella typhimurium with a concentration of 1.5×109 CFU/mL on 8 to 9 days.Sty group:1 mL of 1.5×109 CFU/mL Salmonella typhimurium was given in 8～9 days.The Control group was given PBS for 8 to 9 days,and was free to eat and drink at other times.The body weight of chicks was measured 5 days after challenge,the changes of immune organ index were recorded,the number of viable Salmonella typhimurium in liver,spleen and cecum was detected,and the pathological changes of liver were observed.The results showed that prophylactic addition of Lactobacillus plantarum GX20200417-1 or commercial complex probiotics could slow down the weight loss caused by Salmonella typhimurium infection(P<0.05),reduce the number of Salmonella typhimurium in liver,spleen and cecum(P<0.05),and reduce the pathological damage of Salmonella typhimurium on liver.Finally,16S rRNA high-throughput sequencing was used to analyze fecal flora of chicks five days after infection.The results showed that commercial complex probiotics could decrease the relative abundance of Anaerotruncus and increase the relative abundance of Colidextribacter and Lactobacillus(P<0.05).Lactobacillus plantarum GX20200417-1 could improve the relative abundance of Lactobacillus and resist the invasion of Salmonella typhimurium.3.Effects of Lactobacillus plantarum GX20200417-1 on the immunity and intestinal function in chicksA total of 225 1-day-old healthy yellow-feathered broilers were randomly divided into 3 groups(LP group,S group and Control group)with 5 replicates per group and 15 broilers per replicate.The Control group was fed a basal diet without probiotics,the LP group was fed a basal diet supplemented with Lactobacillus plantarum GX20200417-1(1.5×109 CFU/each)viable bacterial solution,and the S group was fed a basal diet supplemented with 1.5×109 CFU/each commercial complex probiotics in drinking water.The whole experiment period was 42 days.The results showed that Lactobacillus plantarum GX20200417-1 and commercial complex probiotics significantly reduced the ratio of feed to gain of broilers(P<0.05),improved the humoral immune function of broilers,and enhanced the immune effect of Newcastle disease and Avian influenza vaccines.The ratio of villus length to crypt depth was significantly increased(P<0.05).In addition,Lactobacillus plantarum GX20200417-1 significantly increased the mRNA expression of CLDN,MUC2 and TLR2 in jejunum,but the mRNA expression of Occludin,ZO-1 and TLR4 had no significant changes(P>0.05).Commercial complex probiotics significantly increased the mRNA expression of CLDN,Occludin,MUC2,TLR2 and TLR4 in jejunum(P<0.05),while ZO-1 content had no significant change(P>O.05).In terms of the effect on the relative abundance of intestinal flora,probiotics maintain intestinal health of broilers by regulating the relative abundance of specific bacteria in intestine,and Lactobacillus plantum GX20200417-1 promotes the proliferation of pseudoifractor.The proliferation of Parabacteroides and Romboutsia was increased by commercial probiotics(P<0.05).In conclusion,Lactobacillus plantarum GX20200417-1 has excellent biological characteristics,good bacteriostatic effect in vitro,and good degradation effect on gibberellin and aflatoxin of maize.It has good effect on anti-salmonella typhimurium infection,improving immunity and maintaining intestinal health of chicks in vivo.This study provides a theoretical basis for the research and development of Lactobacillus plantarum GX20200417-1 as a substitute for antibiotics and a feed additive. |
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