Abstract: In this study, tricine-sodium dodecyl sulfate-polyacrylamide gel electrophoresis (TSDS-PAGE) was used to determine the molecular mass of an antimicrobial peptide from grass carp scale. Chessboard dilution method was used to determine the combined antimicrobial effect of the peptide and cinnamon essential oil on common foodborne pathogenic bacteria, and the growth curves, cell membrane permeability, and extracellular lactate dehydrogenase activity of the tested strains when exposed to combinations of the two antimicrobials were measured. In addition, flow cytometry was used to analyze the membrane penetration efficiency. The results showed that combination of the peptide, with a molecular mass of 14.3 kDa, and cinnamon essential oil exerted a synergistic effect against Staphylococcus aureus, Vibrio parahaemolyticus and Penicillium chrysogenum and additive effect against Salmonella choleraesuis, Escherichia coli, Aspergillus niger, Mucor wutungkiao, Rhizopus and Saccharomycetes, but had no antagonistic effect on all tested bacteria. Through flow cytometry analysis, it was found that the membrane penetration efficiency of the antimicrobial combination was 72.76% for Staphylococcus aureus, 61.56% for Penicillium chrysogenum, and 51.04% for Vibrio parahaemolyticus, all of which were significantly higher than those of either antimicrobial alone. The antimicrobial mechanism may be by shortening the logarithmic growth period, accelerating the occurrence of the decline period, changing the permeability of the cell membrane, and consequently leading to leakage of intracellular electrolytes and lactate dehydrogenase and subsequent cell death.

Key words: antimicrobial peptide; essential oil; combined antimicrobial activity; antimicrobial mechanism