Screening And Probiotic Characterization Of Several Lactic Acid Producing Strains

Lactic acid bacteria is a type of Gram-positive bacteria which can ferment carbohydrates into lactic acid. Such bacteria are widely distributed in nature, and play an important role in many other areas of human life which is closely related to a number of industrial, agricultural, medical industries and so on. Biologists have confirmed that there is a very close relationship between lactic acid bacteria in intestinal and health and longevity. Numerous studies have shown that probiotics can enhance human health, and have the ability of the prevention and treatment of certain diseases. Therefore, they are often added to foods as a viable agent. The goal of this project is to study by in vitro experiments and animal models to identify and study the characteristics of probiotics about six lactic acid bacteria isolated from the silage. By16S r DNA sequence analysis and phylogenetic taxonomy identification, L1was confirmed belong to Lactobacillus rhamnosus, other five isolates belong to Enterococcus. We analyzed their metabolites by high performance liquid chromatography; conducted safty assessment by detecting virulent factor and antibiotic resistance; tested the survival capability through stomach acid and bile tolerance. The intestinal epithelial cell adhesion and competitive exclusion towards pathogenic E. coli adhesion to epithelial cells were observed. Their capability of degrading cholesterol and induction of inflammatory cytokines were investigated. Finally, biological activity and safety of the strain L1was detected in the mouse model.The results showed that lactic acid is the major metabolite in the six isolated strains. All of them were sensitive to most antibiotics, including tetracycline and vancomycin which is relevant to clinical. They were survival to low pH, bile tolerance and other gastrointestinal conditions. L1, L2, L5have strong adhesion capabilities and can inhibit pathogen adhesion to intestinal epithelial cells. L1and L2can induce inflammatory cytokines to regulate immune response, however does not cause the body injury. Lactobacillus rhamnosus L1was selected to study its probiotic potential and safty in vivo.It was found that L1can increase the relative number of the CD3+, CD4+and CD8+T cell population, thus improving immunity. The results showed that Lactobacillus rhamnosus L1can be used as potential probiotic, and may help improve the body’s immune level. Enterococcus L2may also be used as probiotic candidate, but also need a further in vivo test to verify the safety and functionality.