Abstract: To explore the antibacterial effect and mechanism of LL-1 against Salmonella. Firstly, the minimum inhibitory concentration (MIC) of LL-1 against Salmonella was determined by the doubling dilution method, and the antibacterial effect of LL-1 on Salmonella was evaluated by the antibacterial curve. Then, the bacterial morphology was observed using scanning and transmission electron microscopy. The effects of LL-1 on the cell wall and cell membrane of Salmonella were evaluated by detecting the leakage of nucleic acid, protein and alkaline phosphatase (ALP) and PI staining experiments. The binding of LL-1 to Salmonella DNA was detected by nucleic acid gel electrophoresis. Finally, the effects of LL-1 on the energy metabolism of Salmonella were evaluated by measuring the activities of intracellular succinate dehydrogenase (SDH), NADP-malate dehydrogenase (NADP-MDH) and ATP levels. The results showed that the MIC of LL-1 against Salmonella was 6.25 μg/mL, and LL-1 had a good antibacterial effect and presented dose and time dependence. Salmonella treated with LL-1 showed morphological changes such as shrinkage, cell membrane dissolution, and parenchymal separation. LL-1 resulted in the leakage of intracellular nucleic acids, proteins, ALP and the increase of intracellular fluorescence intensity after PI staining in Salmonella. Additionally, LL-1 could bound with DNA. With the increase of LL-1 concentration, it was decreasing for the intracellular ATP content, SDH and NADP-MDH activities in Salmonella. In conclusion, LL-1 could increase the permeability of Salmonella cell membrane and cell wall, cause content leakage, bind to DNA, and affect bacterial energy metabolism, which lays a foundation for further research on the antibacterial mechanism and application of LL-1.

Key words: Salmonella, antimicrobial peptides, antimicrobial mechanisms, foodborne pathogens, cell membrane, energy metabolism