Isolation and evaluation of bacteriophage lysate specific for Listeria monocytogenes

Listeria monocytogenes is a Gram positive facultative intracellular organism and food borne infective agent that can effect severely to humans and animals. Listeria monocytogenes primarily causes infectious disease such as meningitis, septicemia, and meningoencephalitis that leads to 20 to 25% of death rate in humans. Ingestion of L. monocytogenes contaminated food such as meat, eggs, dairy products, fruits and vegetables leads to serious infectious disease Listeriosis. Most common sources of L. monocytogenes transmission are raw milk, dairy products and dairy plant contaminated by sick farm animals and rarely from the contaminated environment. Bacteriophages specific for Listeria monocytogenes may have a potential role in elimination of sources of contamination. This study was designed to isolate L. monocytogenes specific bacteriophage for lysing the isolate of L. monocytogenes from raw milk using fraser broth. Gram staining, hemolysis test on sheep blood, catalase test and sugar fermentation test were used to confirm colonies grown on plate. The colonies were further streaked on trypticase soy yeast extract and showed white shiny glass like appearance. Isolation and confirmation of bacteriophages was performed by plaque assay method. Abundant of phages are analyzed in sewage water which are vulnerable and extremely flexible host for the presence of Listeria phages. The overall results showed that out of 500 samples of raw milk from five different dairy farms 100 each, 80%, 60%, 32%, 54%, 85% were positive from dairy farm 1, 2, 3, 4, 5 respectively. Five sewage samples were subjected to plaque assay and lysate was prepared. The plaques formed by phages appeared in the form of spherical zone which varies in size and showed lysis of L. monocytogenes. The number of PFU from phage lysate was ranging from 1×103 to 1×106 and estimate plaque size was 0.2±0.5. These results demonstrate application of phages in food industry. Phages can be used individually or in combination as well for the treatment of bacterial infections by targeting cell lysis due to its lytic potential.