Publications

Food-borne diseases caused by pathogens, such as Staphylococcus aureus and Listeria monocytogenes, have for a long time attracted intensive worldwide attention from scientific researchers, food industries, and food safety authorities. Nisin (NS) is the only bacteriocin used worldwide as a GRAS food preservative, while citric acid (CA) has an unrestricted use in foods since it has GRAS status. In this study, synergistic interactions of NS combined with CA against S. aureus and L. monocytogenes were studied by the checkerboard microdilution method, with fractional inhibitory concentration index values ranging from 0.25 to 0.375, and 0.19 to 0.375, respectively. The positive interactions were verified by time-kill studies in pasteurized milk and disc diffusion assays. The mechanism of the synergistic antibacterial of NS and CA is proposed following scanning electron microscopy (SEM) analysis and the determination of release of cell constituents. These results suggest that the cell walls and membrane are the probable main targets of this antimicrobial combination. These findings indicated that the combination of NS and CA could not only be used as a new promising naturally-sourced food preservative but also reduce the problem of bacterial resistance.