Application of phages to an immature bacterial lawn by dropping a small volume such as 10 µl onto the surface of a plate.
Spotting can be used to provide a first approximation of the ability of a phage to lyse (or just kill) a bacterial strain such as during phage typing procedures or, at lower phage densities, as a means of phage titering that is less materials intensive than full-plate assays.
Spotting should not be confused with plaquing, even though spotting can be a means of generating plaques. In particular, a spot in which clearing is confluent (effectively no bacteria across the area of the spot) is not a plaque, and this is because while a plaque starts with one or only a few phages and is formed via repeated rounds of phage infection and bacterial lysis, a spot that starts with numerous phages (as is often the case) produces confluent clearing solely through inhibition of bacterial replication.
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