Screening Of Lactobacillus Plantarum With Potential Inhibition Activity To The Foodborne Enteric Pathogens

This study take 347 strains of Lactobacillus plantarum which isolated from traditional fermented food of Inner Mongolia, Xinjiang, Qinghai, Tibet, Gansu, Yunnan, Sichuan and Mongolia as research subjects. By using the activity of inhibiting foodborne enteric pathogens of Escherchia coli O157:H7, Salmonella typhimurium, Shigella flexneri, Staphylococcus aureus and Listeria monocytogenes as criteria, fourteen isolates with broad-spectrum inhibition to foodborne enteric pathogens were screened for further experimentation. Subsequent assays based on physical, chemical, protease sensitivity, and sensory evaluations of yoghurts fermented in the presence or absence of each of the selected isolates and persistence of antibacterial activity, and the resistance of the strains to simulated gastrointestinal fluid, bile salts were studied. The main experimental results are as follows:Three hundred and forty-seven strains of L. plantarum with a inoculum of 2% were fermented for 24 hours under the conditions of 37℃ in fermented milk, than, those L. plantarum grown in de Man, Rogosa, and Sharpe (MRS) broth at 37℃ for 24 h. All strains were subcultured and grown at 37℃ for 24 h in fermented milk to experiments. The supernatant of each bacterial strain was passed through a sterile syringe filter. By using the well-diffusion agar assay, the result were that there were 65 screened strains showing varying degree of antibacterial activity against the 5 chosen indicator foodborne enteric pathogens. Among these, supernatant of whole milk of 56 strains showed antibacterial activity against Escherichia coli O157:H7, and 31 were good, the diameter of inhibition zone greater than 12mm. There were supernatant of whole milk of 17 strains inhibit Staphylococcus aureus and 16 were good. There were 27 supernatant of strains inhibit Listeria monocytogenes and 18 were good.there were 24 supernatant of strains inhibit Salmonella typhimurium and 20 were good, there were 28 supernatant of strains inhibit Shigella flexneri and 21 were good, From these strains, there were supernatant of whole milk of 13 strains inhibit 5 indicators and there were 2 supernatant of strains inhibit 4 indicators well. In primary screening, taking inhibit 4 kinds of indicators better or 5 kinds of indicators as standard, fourteen L. plantarum with broad-spectrum inhibition to foodborne enteric pathogens were screened for further experimentation.Based on physical, chemical, and sensory evaluations of yoghurts fermented in the presence or absence of each of the selected isolates and persistence of antibacterial activity following protease challenge revealed that the L. plantarumIMAU80184, L. plantarumIMAU10216, L. plantarumIMAU70164 were superior to the other isolates. The fermented supernatant of L.plantarumIMAU80184, L. plantarumIMAU10216, L. plantarumIMAU70164 had broad-spectrum inhibition to foodborne enteric pathogens, And found that enhanced antibacterial activity, better stability to protease through complex fermentation supernatant, and the strain showed well tolerated to gastrointestinal fluid and bile characteristics. To conclude, L.plantarumIMAU80184, L. plantarumIMAU10216, L. plantarumIMAU70164 were identified as excellent strain. We have identified novel bioactive antibacterial L. plantarum with potential for use as a probiotic in the production of fermented milk or other related dairy products. Further in vivo studies are now required.