| The research was aimed to discuss the antibacterial activity and antibacterial mechanism of plum extract, gallnut extract and compound plum extract on pathogenic bacteria. Besides it was also studied the drug resistance of E.coli and the reversal of herbal extracts to drug-resistant E.coli. It would have a theoretical basis for proposing a reasonable strategy to restrict antibiotics used in feed.Research methods:1.We conducted bacteriostatic tests in vitro by Oxford-cup method on Escherichia coli, Salmonella enteritidis, and Staphylococcus aureus, while diameter of inhibition zone was used as the evaluating indicator. On the other hand, the tube dilution method was used to test the MIC(the minimum inhibition concentration)to pathogen. We use these methods to determine the pathogens susceptibility to antimicrobial agents.The antibacterial mechanism of herbal extracts was studied from protein content and the integrity of the cell membrane and cell wall. Bacteria treated by herbal extracts with the concerntration of 1/2、1 and 2 times of MIC. Determine of content of AKP in bacterial broth in order to illustrate the effect of herbal extracts to cell wall. Leaked amount of nucleic acids and ion leakage were determined by spectrophotometric method and Calcium Assay Kit, leaked amount of intracellular proteins were determined by Total protein quantitative assay kit, and compared with blank group.2. E.coli in continued culture under the low drug concentration, use Oxford-cup method and tube dilution method to determine the pathogens susceptibility to antimicrobial agents.Then observe whether E.coil have obtained drug resistance.3. Drug-resistant E.coli in continued culture under the low drug concentration, use the circle of inhibiting bacterium and the minimum bacteriostasis concentration as an index, then observe whether drug-resistant bacteria resistance have reversed.The results were as follows:1.Bacteriostasis experiment in vitro results show that the three kinds of herbal extracts can inhibite the growth of pathogenic bacteria, bacteriostasis of plum extract was more outstanding.Preliminary exploration of herbal extracts of antibacterial mechanism, we found that bacteria treated by herbal extracts, conductivity, macromolecular substance content, calcium ion concentration, AKP content and soluble protein content in bacteria culture had increased. The results showed that the herbal extracts play a role in destroying the integrity of the cell membrane, wall and protein. And compound plum extract mainly affected the cell membrane permeability, while gallnut extract worked on influencing the content of soluble protein and the integrity of the cell wall to work. Besides, the antibacterial mechanism of plum extract remains to be further discussed.2. Results of the resistance test showed that E.coil which continued culture under the low antibiotic concentration can obtain resistance. But the drug resistance of E.coli treated by herbal extracts appeared unconspicuous.3. Through the results of the reverse test, we found that three kinds of herbal extracts can reduce the degree of E.coil resistance of antibiotic partly, but can not reverse bacteria resistant to antibiotic completely.Conclusion:As with antibiotics, herbal extracts can inhibit the growth of pathogenic bacteria, Its mechanism is through selective permeability change bacteria, lead to bacteria caused by leakage of intracellular protein and ion. But continued culture under the low drug concentration, E.coil almost can not obtain resistance,but the bacteria resistant to antibiotic can not reversed. So we should screen other herbal medicines which have bacteriostatic effect acting on drug resistant strains, then discuss the tolerance of drug resistant strains, in order to obtain herbal extracts that have reverse effect.And it would provide a theoretical basis for the development of bacterial resistance inhibitors and reversal agents. |
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