| Hypercholesterolemic is a major risk factor associated with coronary heart diseases, and it isconsidered that keeping blood cholesterol at a desirable level is one of the major preventive strategiesfor these diseases. Thus, much attention has been given to the relationship between diet and bloodcholesterol levels. The main content of this thesis is the further screening of lactic acid bacteriaisolated from traditional dairy products in Inner Mongolia, using the standard which is included fourindexes of the tolerance to simulated artificial gastric juice, hydrophobic capability and deconjugationof sodium taurocholate. A potential strain of lactic acid bacteria with comprehensive performance andexcellent cholesterol-lowering ability was filtered out, the biological characteristics, safety and theapplication of rats in vivo was studied, lay a scientific theoretical basis for further development andapplication of strain.The cholesterol-reducing ability was tested on4strains of lactic acid bacteria by theo-phthalaldehyde method. These isolated strains were incubated in MRS-THIO-OX-CHOL mediacontaining100g/mL cholesterol under anaerobic condition. Cholesterol removal ratio varied amongstrains and ranged from42.47to58.32%. Strain90-1has the highest ability to remove cholesterolfrom media. Four strains of lactic acid bacteria were identified by16S rDNA sequences homologyanalysis. Strain90-1and strain L39-1were identified as Enterococcus faecium, strain L46-2wasidentified as Enterococcus faecalis, strain L46-3was identified as Lactobacillus plantarum.Four strains of lactic acid bacteria were studied for their survival ability in acid and highconcentration of bile salts in vitro under conditions that mimic the human gastrointestinal tract. Fourstrains of lactic acid bacteria showed high acid resistance and bile salt tolerance. They could stillmaintain very high viable cell count after passing through the stomach to the intestine. The finalviable bacterial counts were more than4.7×107cfu/mL after24hours. Under the conditions used inthis study, Enterococcus faecium90-1exhibited strong resistance to gastrointestinal juice. An agarplate assay was developed to detect bile salt hydrolase activity in lactic acid bacteria. Results showedthat the4strains also exhibited bile salt hydrolase activity for a white circle of precipitation. Theability of the strains to deconjugate bile salts was determined as the amount of cholic acid released.Varying amounts of cholic acid were liberated, ranging from2.43to3.35mM. Enterococcus faecium90-1showed strong bile salt deconjugation. Take into account the four rules above, Entercoccusfaecium90-1was evaluated as a potential probiotic with cholesterol-lowering effect. The growth characteristic of the strain90-1was studied. It grew at optimal temperature37℃. Asfor initial pH value for cell growth, the optimal value ranged from5to7. The growth of Enterococcusfaecium90-1culture was tested in MRS medium. It was found Enterococcus faecium90-1beganlogarithmic stage and maximum growth at2h and12h, respectively. Enterococcus faecium90-1had awide antimicrobial activity to Escherichia coli, Staphylococcus aureus and Lester bacteria.Kirby-Bauer method was used as drug sensitive test to the Enterococcus faecium90-1, and6standarddrug sensitive slips were selected in the test, demonstrate that the strain have no resistance to6antibiotics. No reaction was observed around the colonies of Enterococcus faecium90-1on BloodAgar Base Plates, verdict that the strains lack in hemolytic activity.The objective of this study was to evaluate the effects of Enterococcus faecium90-1oncholesterol-lowering of rat in vivo. The rats were fed a commercial chow for1week. After thisadaptation period, rats were divided into three groups of eight each: group A fed with commercialchow, group B fed with high-cholesterol diet only and group C fed with high-cholesterol diet andEnterococcus faecium90-1. At the end of the28days experimental period, blood samples werecollected from the heart under diethylether anesthesia. Serum total cholesterol (TC), triglycerides(TG), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C),liver cholesterol (TC), fecal total cholesterol (TC) and fecal bile acid (TBA) were measured. Afterbeing fed Enterococcus faecium90-1for4weeks，the total cholesterol of rats serum and totalcholesterol of rats liver decreased great significantly (p<0.05); the total cholesterol and bile acid ofrats faecal increased; triglycerides, high-density lipoprotein cholesterol and low-density lipoproteincholesterol almost no change in relatively. This study has demonstrated that the Enterococcus faecium90-1was capable of producing a lipid-lowering effect in hypercholesterolemic rats. |
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