Screening Of Probiotics Against Salmonella Typhimurium And Its Mechanism

Salmonella typhimurium is a foodborne pathogen which has serious harm to humans and animals.Traditional antibiotic therapy has caused a series of problems such as Salmonella resistance and intestinal flora imbalance.Probiotics possess natural activities and most of them can suppress a vast number of foodborne pathogens without side effects,which is gradually being concerned by the public.In this study,Bifidobacterium breve YH68 was screened from 8 probiotic strains,and its cell-free supernatant(CFS)exerted excellent inhibitory activity against S.typhimurium,and the diameter of inhibition zone reached(22.27±0.44)mm.The results indicated that the organic acids and some protein antibacterial substances play critical roles during the process of the antibacterial activity.The minimum inhibitory concentration(MIC)and sub-inhibitory concentration(SIC)of YH68 CFS against S.typhimurium were determined by microdilution method respectively.To explore the antibacterial mechanism of YH68 CFS against S.typhimurium,the cell morphology,cell membrane permeability and integrity changes of S.typhimurium were detected by scanning electron microscope,conductivity measurement as well as confocal laser scanning microscope.The effect of YH68 CFS on the pathogenicity of S.typhimurium was investigated by RT-PCR and cell assay.The results showed that the antibacterial mechanism of YH68 CFS at the MIC value(250 ?L/mL)against S.typhimurium included the increasing of the membrane permeability,the destruction of its integrity,the leakage of intracellular substances,subsequently caused abnormal growth of S.typhimurium.However,the growth of S.typhimurium was not inhibited by YH68 CFS at the concentration of SIC value(62.5 ?L/mL),whereas this concentration weakened the infection effect of S.typhimurium on host cells through downregulating the expression levels of its virulence genes.The CFS of Bifidobacterium breve YH68 in this study exerted an excellent antibacterial activity against S.typhimurium.YH68 could be used as an effective probiotic strain in the prevention and treatment of the infection induced by S.typhimurium in the areas of food or pharmaceutical industry,it has the potential to become an alternative for antibiotics.