Screening Of Anti-drug Resistant Escherichia Coli Lactic Acid Bacteria And Its Antibacterial Mechanism

Due to the improper use of antibiotics,the problem of bacterial resistance is widely presence.Drug-resistant bacteria easily threaten human health through food used as a carrier.The emergence of drug-resistant bacteria has become a focus of global public health.Physical,chemical and biological methods are mainly used to control drug-resistant bacteria in food.Compared with physical and chemical methods,biopreservatives,used as an excellent choice for controlling drug-resistant bacteria in food,have the advantages of safety,high efficiency,and resistance to drug resistance.Lactic acid bacteria(LAB),as a new biopreservative,have a broad-spectrum antibacterial effect on harmful microorganisms in food.In the study,LAB with strong antagonistic activity against drug-resistant Escherichia coli were screened from 80 strains LAB,and the antibacterial mechanism was analyzed.The effects of LAB on resistant E.coli in chicken meat was studied by using fresh chicken as a carrier.It aimed to develop a LAB biopreservative against drug-resistant E.coli.The main findings were as follows:1.Strain XCT1-1 with strong antagonistic activity against drug-resistant E.coli was screened from 80 strains LAB,and the inhibition diameter was 20.31 mm.The strain XCT1-1 was identified as Lactobacillus plantarum by physiological and biochemical identification and 16 S rDNA sequence analysis.According to the pH,temperature and protease test,the active substances in crude extract of strain XCT1-1 were preliminarily determined to be bacteriocins.2.The antibacterial mechanism of the crude extract of strain XCT1-1 against drug-resistant E.coli.The minimum inhibitory concentration of strain XCT1-1against drug-resistant E.coli was 6.0 mg/mL.After exposed to the crude extract of strain XCT1-1,crude extract of strain XCT1-1 contained with azithromycin,the extracellular conductivity of E.coli increased,intracellular protein synthesis was inhibited,and intracellular nucleic acid leaked from cells.The effects of crude extract of strain XCT1-1 combined with azithromycin was better than crude extract alone.Scanning electron microscopy images showed that the cell wall and cell membrane of drug-resistant E.coli were damaged by treatment with crude extract of strain XCT1-1,crude extract contained with azithromycin.When E.coli treated with crude extract of strain XCT1-1,the surface of the cell appeared wrinkled,and the latter overall structure of the cell collapsed..3.The antibacterial effects of crude extract of strain XCT1-1,the crude extract of strain XCT1-1 contained with azithromycin on fresh chicken.The number of microorganism and E.coli in chicken meat were effectively inhibited by treatment with the crude extract of strain XCT1-1,crude extract of strain XCT1-1 contained with azithromycin.Additionally,the increase of pH and TVB-N in chicken were effectively delayed,and the antibacterial effects of the crude extract of strain XCT1-1 contained with azithromycin were better than crude extract alone.The crude extract of strain XCT1-1 could prolong the shelf life of chicken at least 2 d,and the treatment of crude extract of strain XCT1-1contained with azithromycin could effectively extend the shelf life of chicken at least 4 d.The results showed that the crude extract of strain XCT1-1 could increase the sensitivity of azithromycin,and have good antibacterial effect on drug-resistant E.coli.