A single plaque was picked from the bacterial lawn and inoculated into the tube containing 100 μl of log phase culture of S. Typhimurium. After incubated at 37°C for 24 h, the bacteriophage-host mixture was centrifuged at 4,500 xg for 10 min and filtered through a 0.45-ìm pore-size membrane filter. The filtrate was subjected to the plaque assay method as mentioned above.