Nisin is a natural anti-microbial agent used as a preservative in heat processed and low pH foods. Its anti-microbial activity is used against a wide range of gram-positive bacteria and their spores, which cause food spoilage. It especially inhibits heat-resistant bacilli, such as B. Stearothermophilus, C. Butyricum and L. monocytogenes. Nisin alone is not effective against gram-negative bacteria or yeasts and molds. Research has shown that Nisin in combination with chelating agents such as EDTA or nonionic surfactants such as Polysorbate 20, shows potent bactericidal activity against gram-negative organisms.