Antimicrobial activity of Nisin on Bacillus cereus and Bacillus subtilis in a food model and their ultra structural investigation

Nisin is the only bacteriocin confirmed by the World Health Organization (WHO) and is used as a natural food preservative. Nisin is classified as a safe component. The study was conducted to evaluate the antibacterial effectivness of nisin on Bacillus subtilis and Bacillus cereus in the commercial barley soup under different temperature conditions. Additionally, using electron microscopy, cellular structures of the concerned bacteria affected by nisin were studied. The logarithm number of vegetative form of Bacillus cereus and Bacillus subtilis treated with different concentrations of Nisin (0.5, 0.25, 0.125 µg/ml) were analysed during 21 days incubation in a commercial barley soup in temperatures 8 and 25 °C. The exams were repeated three times. The cell structure of studied bacteria were analysed under treating with highest concentration of nisin. The logarithm number of bacteria was evaluated under effectiveness of different concentration of nisin, temperature, and the time of incubation using analysis of varians (ANOVA). The result showed that the growth and survival of the bacteria in barley soup were affected by all nisin concentrations. The bacteria were inhibited at 8 °C greater than to that of 25 °C (p<0.05). Pictures of Electron microscopy indicated different degrees of structural damages in cytoplasmic membrane of the bacteria treated with nisin. Nisin shows antimicrobial activity and inhibit the growth of food-born bacterial pathogens in low temperature.