Abstract: The objective of this study was to explore the synergistic antimicrobial effect of Helveticin-M combined with chlorogenic acid against Escherichia coli and Salmonella enteritidis by examining growth curves and cell viability. Furthermore, the morphology, structure and membrane permeability of the indicator bacteria were characterized by scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM) and extracellular ATP analysis. The results showed that the synergistic effect of Helveticin-M combined with chlorogenic acid was markedly increased when compared with either antibacterial agent alone (P < 0.05). The structure of the bacterial cells subjected to the combined treatment was damaged seriously under SEM and CLSM examination, indicating increased permeability of the cytoplasmic membrane. There was a significant difference in extracellular ATP concentration between the combined treatment and either treatment alone (P < 0.05). In conclusion, the combination of Helveticin-M and chlorogenic acid exerted a notable synergistic antimicrobial effect by increasing membrane permeability and thereby leading to the leakage of intracellular components. This study provides a basis for expanding the industrial application of Helveticin-M and chlorogenic acid.

Key words: Helveticin-M, chlorogenic acid, Escherichia coli, Salmonella enteritidis, synergistic effect, antimicrobial mechanism