Isolation And Screening Of Rabbit-derived Lactic Acied Bacteria And Their Alleviation Effect On Dexamethasone-induced Oxidative Stress In Rabbits

Probiotics have a variety of health benefits and play an important role in improving host gut barrier function,immunity and productive performance.Recent research on probiotics has also revealed that they improve the antioxidant capacity of the host in a number of ways.Rabbits are an important source of protein and have a variety of nutritional properties,but under modern intensive farming rabbits are susceptible to oxidative stress,resulting in reduced growth performance and meat quality.In vitro supplementation with probiotic preparations is considered to be an effective way to improve the host’s antioxidant capacity and reduce oxidative stress.Ideally probiotic strains should be selected from homologous animals and tolerate the harsh gastrointestinal environment of the host.Studies on the beneficial properties of probiotics have now been conducted on several species,including pigs,sheep and chickens,and have demonstrated their positive role in host health.However,studies on probiotics in rabbits are limited.Therefore,the aim of this study was to isolate and screen excellent rabbit-derived lactic acid bacteria and investigate their protective effects against oxidative stress in rabbits.The main studies and results are as follows:1.Results of the isolation,screening,identification and biological characterization of lactic acid bacteriaA total of 23 potential candidate bacteria were isolated from rabbit feces,and after sequencing and preliminary screening,four strains of Lactobacillus johnsonii:B2-3;Weissella paramesenteroides:A5-4;Weissella confusa:C6-1;Enterococcus faecalis:C2-3 were identified.In order to investigate the potential probiotic properties of the isolates,acid and bile salt resistance,hydrophobic self-agglutination,inhibition,drug sensitivity,hemolytic and antioxidant tests were performed on the four strains.The results showed that the four strains had good acid and bile tolerance,inhibition,hydrophobicity and self-agglutination,but could not tolerate high temperature of 65℃.Among them,Lactobacillus yohimbe B2-3 showed the highest survival rate in acid and bile salt environment,57.51%and 72.81%,respectively;hydrophobicity and selfagglutination rate,76.23%and 88.2%,respectively;it showed strong inhibitory effect on Escherichia coli,Salmonella enteritidis and Listeria monocytogenes,and the best inhibitory effect on Clostridium perfringens among the four strains,with an inhibition circle diameter of26.19±1.58mm.In addition,the safety test results showed that the isolates were sensitive to most antibiotics and did not hemolyze.In vitro antioxidant assays showed that the isolates were tolerant to H₂O₂and had high DPPH scavenging ability,reducing ability and resistance to lipid peroxidation.Among them,the DPPH radical scavenging rate of Lactobacillus johnsonii B2-3 was 24.42%and the anti-lipid peroxidation rate was 38.6%,which had a strong in vitro antioxidant capacity.2.Protective effects of Lactobacillus johnsonii against dexamethasone-induced oxidative stress in rabbitsMale rabbits were randomly divided into four groups according to the principle of similar body weight:control group（group C）,Lactobacillus johnsonii group B2-3（group B）,dexamethasone group moulding group（group D）,and prophylactic group（group BD）./kg/d)for 23 d.After that,based on the continuation of the prophylactic period,oxidative stress was induced by subcutaneous injection of dexamethasone sodium phosphate injection（2 mg/kg/d）per animal in groups D and BD,and in groups C and B,equal amount of saline was injected subcutaneously per animal daily for 7 d.The total number of test days was 30 days.The results showed that rabbit-derived Lactobacillus johnsonii B2-3 significantly improved the growth and slaughter performance of rabbits and alleviated the negative effects of serum biochemical and antioxidant enzyme dysregulation,liver pathological damage,and impaired intestinal mucosal morphology caused by semimethasone.In addition,Lactobacillus yohimbe pretreatment also modulated intestinal flora and intestinal metabolism thereby reducing the effects of oxidative stress on rabbits.Specifically,supplementation with Lactobacillus johnsonii resulted in a significant increase in the index of alpha diversity of the intestinal flora,accompanied by a significant change in taxonomic composition.Taxonomic analysis of the bacteria showed that at the phylum level,the proportions of Bacteroidota,Verrucomicrobiota and Actinobacteriota were up-regulated.At the genus level,the genera Eubacteriaceae,Akkermansia and Lactobacillus were up-regulated and unclassified＿c＿＿Clostridia was significantly down-regulated.Metabolomic analyses showed that 455 differential metabolites were identified,involving protein digestion and absorption,glycerophospholipid metabolism,autophagy-other,autophagy（GPI）-anchor biosynthesis,and autophagy-animal（autophagy-animal）.Differential metabolites such as phosphatidylethanolamine PE(18:4（6Z,9Z,12Z,15Z）/22:6（4Z,7Z,10Z,13Z,16Z,19Z）,PE（14:0/16:0）and PGP（16:0/20:4（5Z,8Z,11Z,14Z））may also be alleviated by upregulation of oxidative stress in rabbits.In conclusion,the rabbit-derived Lactobacillus johnsonii isolated and screened in this study not only helped to improve the growth performance,slaughter performance and antioxidant capacity of rabbits,but also played an important role in increasing the diversity and abundance of intestinal microorganisms and regulating intestinal metabolism,and the altered intestinal flora and metabolites may be one of the key ways for Lactobacillus johnsonii to exert its probiotic effects.