This protocol explains how phage plated for high titer can be extracted from those plates. Choose the lacey plates for your harvesting.
1.) Using a lacey plate, add 5 mL MP buffer. Allow to sit at room temperature for 2 hours, gently shaking the plates in a radial manner every 10 minutes. This allows the MP buffer to extract the phage a bit better from the media.
2.) After the 2 hour incubation, pipette the phage into a 10 mL syringe with a 0.22 uM filter. Aseptically filter the phage. This is your purified, concentrated phage. A few uL of this can be diluted and plated to determine the Plaque Forming Units (PFU) your sample is capable of making.
Other time periods of incubation of phage with MP buffer will extract phage, the more time the better. A good phage titer can be yielded in an hour or less, however I recommend frequent rocking of the plates (this can be done by hand) to liberate a greater number of the phage from the plate. It is a good idea to piggyback a couple of procedures while harvesting phage, or to designate an individual within a lab group to be the "shaker."