Synergy of a combination of nisin and citric acid against Staphylococcus aureus and Listeria monocytogenes

ABSTRACT

Food-borne diseases caused by pathogens, such as Staphylococcus aureus and Listeria monocytogenes, have long attracted attention globally from researchers, food industries, and food safety authorities. Nisin (NS) is the only bacteriocin used worldwide as a generally recognised as safe (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 chequerboard 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 pasteurised milk and disk diffusion assays. The mechanism of the synergistic antibacterial of NS and CA is proposed following 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 not only could be used as a new promising naturally sourced food preservative, but may also reduce the problem of bacterial resistance.

Graphical Abstract

KEYWORDS:

• Staphylococcus aureus
• Listeria monocytogenes
• nisin
• citric acid
• synergism

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

Financial support for this work came from the following sources: National Nature Science Foundation of China (grant nos. 31271951 and 81573448), China Postdoctoral Science Foundation (2013M530142), the Program for New Century Excellent Talents in University (NCET-13-0245), and Natural Science Foundation of Jilin Province (No. 20150101009JC).