Nisin (or more accurately Nisin A), also known as a lantibiotic, is a small-molecule polypeptide antibiotic with antibacterial activity, synthesized and secreted by Lactococcus lactis subsp. lactis during metabolism.

It is commonly used as a preservative in processed cheeses and meat products to inhibit Gram-positive spoilage and pathogenic bacteria. The European food additive number is E234. Generally, it is safe, natural, vegan (maybe), halal, kosher and gluten-free.

http://www.chinafooding.com/Nisin