Screening Of Plant Phenols Against Salmonella Typhimurium And Its Mechanism Discussion

Food safety is essential to human health.As a common pathogenic bacterium in food,Salmonella causes serious harm and influence to food safety and consumer health.Salmonella has a variety of serotypes,among which Salmonella typhimurium is the dominant serotype,and its incidence of infection is the highest serotype.Currently,the treatment of Salmonella is usually drug treatment,but the use of traditional treatment can induce drug resistance,cause intestinal flora disorders and other problems.In recent years,many studies have confirmed that plant polyphenols have broad-spectrum antibacterial properties.They have the advantages of natural and no side effects in the prevention and treatment of foodborne pathogens.This new microecological therapy is gradually attracting public attention.Therefore,in this study,Salmonella typhimurium was selected as the indicator bacteria,17 common polyphenols in daily life were selected,and resveratrol,an active substance with good antibacterial effect,was initially screened out,and its inhibitory mechanism against Salmonella typhimurium was further explored from the cellular and metabolic levels.To provide a theoretical basis for the control of plant polyphenols against Salmonella typhimurium in food industry,medicine industry or aquaculture industry.The main research contents were as follows:1.Screening of plant polyphenols against Salmonella typhimuriumKanamycin sulfate was used as positive control.The antibacterial activity of 17 polyphenols was screened by agar diffusion method,multiple dilution method,bacteriostatic rate and IC50 value,and the antibacterial effect was observed by growth curve.The results showed that the inhibitory effect of resveratrol was better.The minimum inhibitory concentration of resveratrol was 250 μg/m L,the inhibitory rate of resveratrol reached 96.53%,and the IC50 value was 136.70 μg/m L.The growth curve showed that the delay period of the strain was prolonged,the exponential growth rate was decreased,and the normal growth cycle of the bacteria was broken,thus exerting an inhibitory effect.2.Inhibitory mechanism of resveratrol against Salmonella typhimurium based on cell level analysisThe bacteriostatic mechanism of resveratrol was further studied by measuring cell wall integrity,cell membrane permeability,biofilm formation ability and electron microscopy.The results showed that: when Salmonella typhimurium is treated with resveratrol,the extracellular alkaline phosphatase content could reach 3.31 Kim unit/100 m L,the cell membrane potential was significantly decreased（P<0.01）,the conductivity in culture medium was 13.43 ms/cm,the Na⁺ content was 149.06 mmol/L,the K+ content was 18.90 mmol/L,and the Mg²⁺ content was 0.13 mmol/L,protein content 4.51 mg/m L,nucleic acid release significantly increased and the biofilm formation ability significantly decreased（P<0.01）.By scanning electron microscopy（SEM）and transmission electron microscopy（TEM）,the surface of thalli showed different degree of damage,surface fold and collapse were obvious,and the morphology was seriously damaged.This confirmed that resveratrol can cause the death of bacteria by damaging the cell wall and cell membrane structure,leading to the leakage of materials inside the bacteria.3.Mechanism analysis of resveratrol against Salmonella typhimurium based on metabolic levelThe changes of metabolites of Salmonella typhimurium treated with resveratrol and related metabolic pathways were analyzed by Gas chromatograph-mass spectrometer（GC-MS）technology,and a new clue was provided for the antibacterial mechanism of resveratrol from the point of metabolomics.The results showed that the metabolites of Salmonella typhimurium treated with resveratrol were significantly different from those of normal strains.A total of 23 different metabolites were screened,mainly organic acids,sugars and other substances.KEGG metabolic pathway analysis showed that resveratrol had significant effects on eight metabolic pathways,among which the significant effects included arginine and proline metabolism,alanine,aspartate and glutamate metabolism,butanoate metabolism,and nicotinamide and nicotinamide metabolism.The disturbance of these metabolic pathways made the energy metabolism of Salmonella typhimurium unbalanced,the synthesis of nucleic acid was affected,the cell wall and membrane were damaged,and the inhibiting effect of Salmonella typhimurium was achieved finally.