| [Objective]Nowadays, with the perceptible improvement of living standard, people's demand for food nutrition is increasing. At the same time, some negative effects are accompanied, such as atherosclerosis, coronary heart disease, high blood pressure and other cardiovascular or cerebrovascular diseases. Many clinical trials confirmed that orally taking Lactic Acid Bacteria (LAB) and their related products could not only reduce the serum cholesterol concentration but also reduce the risk of suffering from cardiovascular disease. This study was going to screen several cholesterol-lowering lactic acid bacteria strains and investigate their probiotic properties. Cholesterol-lowering mechanism in vitro and vivo would also be examed. The cholesterol-lowering strains and research papers can promote the devepment of functional lactic acid bacteria and supply an application research support.[Methods]Original LAB strains were screened based on the calcium carbonate-MRS medium (calcium carbonate-Man Rogosa and Sharp Medium) from Chinese tradition pickles and sausage. The cholesterol-lowering strains were confirmed by screening with in vitro cholesterol levels. They were identified by morphologic observation, catalase reaction, carbohydrate reaction and 16SrRNA sequencing. Their acid resistances, bile salts resistance activity, growth curve, acid producing properties, sensitivity to antibiotics, inhibitory effect on common pathogenic bacteria, degradation of cholesterol and co-precipitation of cholesterol action in vitro had been systemic studied. Hyperlipidemia rats were introduced by being fed of fat-rich diet and then be fed of strain everyday, and we traced the change in serum to access their cholesterol-lowering activity in vivo.[Results]Two strains LpT1 and LpT2 were obtained and identified as Lactobacillus plantarum, their cholesterol degradation ratio were 49.11% and 50.03%, respectively. Lactobacillus plantarum LpT1 and LpT2 showed high acid resistance and bile salt tolerance. Lactobacillus plantarum LpT1 could survive at least for 8 hours under pH 3.0 and for 8 hours in the medium containing 0.3% bile salt, while Lactobacillus plantarum LpT2 could survive for 6 hours and 8 hours under the same condition. LpTl reached the logarithm phase of growth and stationary phase of growth at 14th hour and 22th hour after been cultivated, while LpT2 at 12th hour and 20th hour after been cultivated. The final pH values were 4.2 and 4.0 after cultivated for 30 hours. Both of them were sensitive to the 18 kinds of antibiotics and their diameters of inhibition zone were more than 20 mm. The fermentation supernatant could significantly inhibit Salmonella, Pseudomonas aeruginosa, Staphylococcus aureus, and Escherichia coli.There was no significant difference in cholesterol-reducing activity of Lactobacillus plantarum LpT1 and LpT2 whether the culture medium contained coalescent bile salt sodium taurocholate or not. There was a significant difference in cholesterol-lowering activity when Lactobacillus plantarum LpT2 liveed in the medium with bovine bile salt or without (p<0.05). Hyperlipidemic rat model was built successfully through being fed fat-rich diet for 7 days; After being fed strain LpT1 for 4 weeks, the total cholesterol of rats serum decreased great significantly (p<0.01), triglyceride decreased significantly (p<0.05), high-density lipoprotein cholesterol almost no change in relatively, low-density lipoprotein cholesterol decreased significantly (p<0.05), arteriosclerosis index decreased significantly and HDL-C/TC value increased obviously. After being fed strain LpT2 for 4 weeks, the total cholesterol of rats serum decreased significantly (p<0.05), low-density lipoprotein cholesterol decreased significantly (p<0.05), triglycerides declined indistinctively. The results showed that after being fed Lactobacillus plantarum and lovastatin, rats'weight gain rate was lower significantly than those being fed with distilled water.[Conclusion]The results showed that both Lactobacillus plantarum LpT1 and LpT2 had a high cholesterol-lowering activity in vitro and a positive effect on hyperlipidemic rats in vivo. The strains also could slow down the utilization of fat-rich diet to alleviate the weight gain simultaneously. In addition, there was no obvious correlation between cholesterol-lowering activity and the existence of bile salts in medium or not. However, composition of bile salts could affect cholesterol-lowering activity. In case to co-precipitation and assimilation, there was some complicated metabolic degradation mechanism. After bacterial colonized in rats gut, it could produce specific metabolites or enzymes to act on liver through direct or indirect ways. In conclusion these two strains showed a potential applied value.
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