Armita Azad - Department of Microbiology, Falavarjan Branch, Islamic Azad University, Isfahan, Iran
nafiseh naghavy - Falavarjan Branch, Islamic Azad University, Isfahan, Iran
vajihe Karbasizade - Department of Microbiology, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran

Among lactic acid bacteria (LABs), Lactococcus lactis has been much concerned because of its acceptable stability and bacteriocin (nisin) production. This study was aimed to investigate the antibacterial effects of bacteriocin produced by Lactococcus lactis isolated from native dairy products against some foodborne pathogenic bacteria and to optimize its production conditions. First, ۱۵ strains of Lactococcus lactis were isolated from sheep and goat milk samples in M۱۷ culture medium and identified by biochemical and molecular methods. Then, the optimal conditions for bacteriocin production by Lactococcus lactis were determined using Taguchi statistical method in terms of pH, temperature and production time. Evaluation of the antimicrobial activity of bacteriocin produced against standard strains of foodborne pathogens was evaluated by well diffusion method. Cell-free supernatants were obtained from Lactococcus lactis I۸ from goat milk showed antimicrobial activity against Shigella flexneri, Salmonella typhimurium, and Staphylococcus aureus strains; While Escherichia coli showed resistance to the bacteriocin. Optimal bacteriocin production by Lactococcus lactis was done at pH = ۷, temperature of ۲۶ °C and ۲۲ h incubation period. The high antibacterial activity of this bacteriocin against putative pathogens such as Salmonella typhimurium and Shigella flexneri would make it a good candidate as a probiotic strain to be used for treatment of infections caused by these bacteria, and also the application possibility of the produced bacteriocin as a suitable food preservative is proposed.

bacteriocin, Salmonella typhimurium, Shigella flexneri, Foodborne pathogen, Staphylococcus aureus