2.2. Phage Propagation and Purification

Phage propagation and purification were performed using the DLA assay in accordance with a previously described protocol with minor modifications [23]. The 18 h cultured top agar was collected using SM buffer (100 mM NaCl, 50 mM Tris (pH 7.5), and 10 mM MgSO₄) and centrifuged to isolate phages from the agar matrix, after which it was filtered through a 0.45 μm membrane filter. Precipitation using ammonium sulfate was performed for the purification of phages. The phage lysate was mixed with 2% (v/v) Tween-80, and 35% (w/v) ammonium sulfate, and was incubated for 15 min at 4 °C. The pellicle was resuspended in SM buffer and purified using CsCl gradient ultracentrifugation [23]. The high titer of phage suspension (>10¹⁰ plaque-forming units (PFUs)/mL) dialyzed using 7000 MWCO membrane was stored at 4 °C.