مشخصات پژوهش

Listeria monocytogenes is an opportunistic food- borne pathogen which can cause a severe disease known as listeriosis. Despite the low incidence, lister- osis is a great concern to public health due its high mortality rate. Bacteriophages as natural enemies of food spoiling pathogens and can expand shelf life of food products. in this study a listeriaphage was iso- lated from environmental samples and its efficiency to use in dairy productswastested. Materials and Methods Listeriophage isolated from environmental samples of a fish market using soft agar overlay method. 100 gr of different dairy products including pasteurized milk, chocolate milk (3.5% fat), mozzarella cheese, ice cream and cream (30% fat) were contaminated with 103 CFU/gr of L. monocytogenes culture (PTCC 130) and incubated at 6°C for 1 h. After phage puri- fication and quanitifaction, 108 PFU/gr phage were added and incubated at 6°C for 6 days. Afterward bacterial viable counts of contaminated foods were tested via surface plating method. cell count differ- ences between controls and phage-treated samples were compared. Results One phage isolated against L.monocytogenes . The application of phage in liquid products, such as milk and chocolate milk reduced final counts of bacteria 3.2 log units. On mozzarella cheese a reduction of 2.2 log units was observed. In the sample of cream the viable bacterial count cells reduced by 2 log units. moderate effect of phage was observed on ice cream with decreases of 1.6 log units. Conclusion Our data indicated that the isolated virulent phage can be effective for biocontrol of L. monocytogenes in contaminated products.