Abstract: To investigate the synergistic antibacterial activity and mechanism of culture supernatant of Lactobacillus paracei Z17 combined with?chitosan against Escherichia coli O157:H7 in strawberry, flow cytometry, Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy and scanning electron microscopy (SEM) were used to study the damage to the cell membrane of E. coli O157:H7 caused by Lactobacillus paracei Z17-chitosan mixture. The results showed that combined treatment with 1.0% chitosan solution and Lactobacillus parace Z17 could decontaminate E. coli O157:H7 on strawberries by 99%. The extracellular release of DNA from E. coli O157:H7 was (381.00 ± 3.53) ng/μL and the proportion of cells with a damaged membrane was 58.3% after combined treatment for 3 h. Fatty acids, proteins, peptidoglycans, glycoside rings and polysaccharides were destroyed in the cell wall membrane. The cell membrane exhibited local displacement and became thinner, and large molecules were adhered to the cell surface, with holes in it, leading to leakage of intracellular contents and eventually cell death. In conclusion, L. paracei Z17-chitosan mixture can inhibit E. coli O157:H7 on strawberries by targeting the cell membrane of E. coli O157:H7, which may be useful for the biocontrol of E. coli O157:H7.

Key words: Escherichia coli O157:H7; Lactobacillus paracei Z17; chitosan; antibacterial mechanism