| In recent years,livestock and poultry diets has received different levels of cadmium pollution in China.Cadmium in feed not only directly harms the health of livestock and poultry,but also causes potential harm to human health through the food chain.The methods currently to prevent and control heavy metal pollution in the ecological environment mainly include physical,chemical and biological methods.Among them,the microbial adsorption method has been widely used in the field of environmental protection due to its advantages of safety,environmental protection,and high efficiency.However,there is still a lack of animal experiments to support whether microbial adsorption can prevent and control cadmium poisoning in animals.In this study,we isolated and screened poultry-derived cadmium-tolerant lactic acid bacteria in vitro,explored the adsorption capacity and probiotic properties of the isolated strains in vitro,and selected the strains with the strongest adsorption capacity for animal experiments,further to investigate the protective effect of selected strains on sub-chronic cadmium poisoning in chickens.From March to June 2020,13 fecal samples of healthy chickens from different farms were collected.Firstly,62 cadmium-tolerant strains were isolated using MRS medium（containing100 mg/L Cd）,and 9 strains were screened by series of cadmium concentrations（200-1000mg/L）.All of 9 strains were identified as lactobacillus by gram staining,bacterial biochemical identification and 16S r RNA sequencing.Secondly,4 strains with the strongest adsorption capacity were selected from 9 strains,and the influence of different physical and chemical factors（p H,time,cadmium concentration,cell concentration）on the ability of lactic acid bacteria to adsorb cadmium was explored.The results showed that:（1）The adsorption effect of4 strains was best at p H=5.（2）With the increase of cadmium concentration,the adsorption rate decreased and the adsorption capacity per unit cell increased.（3）With the increase of the bacterial cell concentration,the strain adsorption rate increased,and the adsorption capacity per cell decreased.（4）With the extension of the adsorption time,the strain adsorption rate and unit cell adsorption capacity increased,and gradually stabilized after 2 h.Finally,the probiotic properties of the 4 strains in terms of acid tolerance,bile salt tolerance,drug resistance and antibacterial effects were explored.The results showed that:4 strains had good acid resistance and could survive in the acidic environment of p H=2.5;4 strains could tolerate 0.3%bile salt at most;4 strains had good inhibitory effect on three common intestinal pathogenic bacteria（Staphylococcus aureus,Salmonella,Escherichia coli）;4 strains were sensitive to cephalosporin,penicillin,lincomycin and amidol drugs,and resistant to tetracycline,fluoroquinolone,sulfonamide and polypeptide drugs.Considering the adsorption capacity and probiotic characteristics,the CLF9-1 strain was selected as the experimental strain for animal protection test.The experiment selected 72 two-week-old Xueshan chickens and randomly divided them into six groups with twelve in each group.They were divided into control group,Cd group（100mg/L Cd）,Cd+Low LAB group（100 mg/L Cd+5×109 cfu/m L LAB）,Cd+High LAB group(100 mg/L Cd+1010 cfu/m L LAB),Low LAB group（5×109 cfu/m L LAB）and High LAB group(1010 cfu/m L LAB).Cadmium exposure was carried out by drinking water,and 1 ml fresh bacterial solution was intragastrically administered daily for 6 weeks.The body weight was weighed every week and the feces of each group were collected to detect the fecal cadmium content;blood was collected to separate serum to determine the activity of related enzymes;the main organs of heart,liver,spleen and kidney were dissected to detect the organ coefficient and cadmium content;the pathological changes of liver,kidney and duodenum were observed.The results showed that:（1）Compared with the control group,Cadmium exposure reduced the weight gain rate of chickens,and the administration of Cd-tolerant lactobacillus alone had a certain promotion weight gain effect on chickens.（2）Compared with the control group,cadmium exposure significantly reduced the liver and kidney coefficients;compared with the cadmium group,the liver and kidney coefficients increased significantly after administering high-dose lactic acid bacteria（p<0.05）.（3）Histopathological observation revealed that cadmium exposure caused liver and kidney damage,including liver congestion,hepatocellular agglutination and necrosis,renal tubular epithelial cell degeneration,and glomerular swelling and other pathological changes;duodenal tissue sections showed that cadmium exposure reduced villus height,increased muscle thickness and crypt depth.Compared with the cadmium group,the liver and kidney injury were alleviated,the villus height was significantly increased,and the muscle thickness and crypt depth were significantly decreased in the cadmium plus low-dose lactobacillus group（p<0.05）;the liver and kidney injury were significantly alleviated,the villus height was significantly increased,and the muscle thickness and crypt depth were significantly decreased in the cadmium plus high-dose lactobacillus group（p<0.01）.（4）Compared with the control group,the activities of AST,ALT AKP and the contents of BUN and CREA in the cadmium group were significantly increased;compared with the cadmium group,the activity of AST in the cadmium plus low-dose lactobacillus group was significantly decreased（p<0.05）,the activities of ALT and AKP were extremely significantly reduced（p<0.01）,the contents of BUN and CREA were reduced,but the difference was not significant;the activities of AKP,ALT,AST in the cadmium plus high-dose lactobacillus group were extremely significantly reduced（p<0.01）,the contents of BUN and CREA were significantly reduced（p<0.05）.（5）Compared with the cadmium group,the combination of cadmium and lactobacillus increased the excretion of cadmium in feces and reduced the cadmium content in the liver and kidney.In summary,this experiment isolated and screened cadmium-tolerant lactic acid bacteria from production,and established an animal model,proving that it has a protective effect on sub-chronic cadmium poisoning in chickens.This research provides a theoretical basis for the development of functional probiotic additives for the prevention and control of heavy metal poisoning in poultry and the reduction of heavy metal pollution in poultry products.Moreover,microbial cadmium adsorption method is efficient,environmental protection,safety,conform to the development trend of animal husbandry that reduces resistance and no resistance. |
PDF Full Text Request