Nisin is a polycyclic antibacterial peptide produced by the bacterium Lactococcus lactis that is used as a food preservative.

In the food industry, nisin is obtained from the culturing of L. lactis on natural substrates, such as dextrose, and it is not chemically synthesized.

[2] While most bacteriocins generally inhibit only closely related species, nisin is a rare example of a "broad-spectrum" bacteriocin effective against many Gram-positive organisms, including lactic acid bacteria (commonly associated with avoiding food spoilage), Listeria monocytogenes (a known pathogen), Staphylococcus aureus, Bacillus cereus, Clostridium botulinum, etc.

Gram-negative bacteria are protected by their outer membrane but may become susceptible to nisin action after a heat shock or when this is coupled with the chelator EDTA.

[3] The mode of action of Nisin against pathogens such as Listeria monocytogenes is to dissipate the membrane potential and pH gradient.