Abstract

Rowaida Khalil, Fatima Djadouni, Yasser Elbahloul and Sanaa Omar

Bacillus megaterium 22, a soil isolate, produced a bacteriocin that exhibited a broad range of inhibitory activity against food-spoilage microorganisms including Salmonella typhimurium and Staphylococcus aureus. The antimicrobial activity peaked at the early stationary phase. De Man Rogosa Shrarpe (MRS) was the best medium for bacteriocin production, where growth of B. megaterium 22 for 12 - 18 h at 30oC, pH 6 - 6.5 resulted in maximum inhibitory effect on the pathogenic indicator strains. Supplemen-tation and/or replacement of medium nutrients demonstrated higher values of bacteriocin activity in the presence of 5 - 10% sucrose, 1% beef extract, and under limited aeration. Bacteriocin activity was significantly stimulated at concentrations of up to 3% NaCl, or 1% KCl. Low levels of spices (curry, red and Black pepper) synergistically stimulated the bacteriocin activity, except for garlic and rosemary where higher concentrations (1%) considerably influenced the activity. The bacteriocin was heat stable for 15 min of exposure to a wide range of temperatures, and over a pH range of 2 - 8 after 1 h of expo-sure. The bacteriocin was stable for up to 30 min of exposure to UV light, and when stored at 4 oC for 90 days. The activity was inhibited by proteolytic enzymes and tested organic solvents. SDS-PAGE revealed that the apparent molecular weight of the partially purified bacteriocin ranged from 3.496 to 6.512 kDa. Results presented here support the idea that the bacteriocin may propose some industrial advantages that render it as a good natural food bio preservative candidate.