Efficacy of a combination of nisin and p-Anisaldehyde against Listeria monocytogenes

• Nisin combined with AS showed synergistic antibacterial activity.
• Time-kill assay was performed in milk.
• Nisin combined with AS may be used in food industry.

Nisin is used as a food-safe antimicrobial agent and has been widely applied to daily food products to prevent bacterial growth. However, the practical application of nisin is limited. Although nisin inhibits the growth of Listeria monocytogenes, exposure to this agent is also a risk factor for the development of nisin resistance. p-Anisaldehyde (AS) is used in the pharmaceutical industry to manufacture antimicrobial drugs, but few studies have been reported describing the antibacterial activity of AS in the food field. Combining nisin with AS may enhance antimicrobial activity. The synergy observed in vitro was confirmed by checkerboard microdilution method, with the fractional inhibitory concentration index (FICI) values ranging from 0.125 to 0.281. When AS was combined with nisin, a strong synergistic effect was observed using the time-kill and agar-diffusion assays. SEM and LIVE/DEAD BacLight experiment results also suggest that the bactericidal mechanism of the drug combination involves cell wall lysis and membrane damage. We can use this synergy to achieve a stable antimicrobial effect to overcome antimicrobial drug resistance.