Nisin

Nisin is a polycyclic lantibiotic bacteriocin produced by Lactococcus lactis subsp. lactis. It acts as a natural preservative in foods by inhibiting Gram-positive bacteria through a dual mechanism: it binds to lipid II, a key component of cell wall synthesis, thereby blocking peptidoglycan formation, and it forms pores in the bacterial membrane. This makes nisin particularly effective against many foodborne and spoilage organisms, including Listeria monocytogenes and several Bacillus and Clostridium species, especially in acidic environments.

Chemically, nisin is a small peptide of about 3.3 kDa that contains unusual amino acids such as lanthionine and methyllanthionine, resulting from post-translational modifications. It features five intramolecular rings (labeled A through E) that contribute to its stability and activity. Nisin is relatively heat-stable and remains active across a range of pH values, though it is susceptible to proteolytic degradation by proteases.

Production and variants: Nisin is produced by fermentation using Lactococcus lactis strains. The most common natural form is nisin A, with other natural variants including nisin Z and nisin F. Commercial nisin is purified from fermentation broth and used as a food additive in various products.

Applications and regulation: Nisin is approved for use as a food preservative in many countries. In the European Union it is listed as additive E234; in the United States it has GRAS status and regulatory approval for use in certain foods. It is widely employed in dairy products (notably cheeses), processed meats, canned vegetables, and some beverages to inhibit spoilage and dangerous Gram-positive bacteria. Its effectiveness is limited against Gram-negative bacteria unless used with other hurdles or permeabilizing agents.

Safety and limitations: Nisin is generally regarded as safe at approved use levels. It is not effective against most Gram-negative bacteria on its own, and resistance can occur with prolonged exposure.