Nisin production conditions optimization and its effect on Bacillus cereus and Listeria monocytogenes

Lactococcus lactis isolate B18, has been selected according to its effect on listeria monocytogenes and Bacillus cereus and were respectively (5-4) mm as inhibition diameters by halls method after pH modification, nisin gene has been recognized by PCR technique, best production medium has been selected and was M17 broth besides to 3% lactose and 3% yeast extract, then production conditions have been optimized and were for listeria monocytogenes and Bacillus cereus respectively (pH 6, temperature 34o C, Incubation time 54 hrs, and inoculation size 1.5 ml), (pH 5.5, temperature 31o C, Incubation time 54 hrs, and inoculation size 1.5 ml). The inhibition diameter became 12 mm against listeria monocytogenes, the inhibition diameter became 9 mm against Bacillus cereus. Over all nisin effect on listeria monocytogenes affected by temperature, Incubation time, and inoculation size. and its effect on Bacillus cereus affected by pH, temperature, Incubation time, and inoculation size