Hello all! I am performing a plaque assay for a phage I isolated from a sewage sample and was wondering if it's normal that lower dilutions show colonies on a fairly clear base (from my understanding it means that the phage concentration is high that's why the bacterial lawn isn't showing). These colonies disappear as dilutions increase to show good plaques on the bacterial lawn. Pictures are attached. Thank you!
Those plates look totally normal where the top plate has too many phages and kills all the host cells that would normally make the lawn. The bottom plate looks great. The colonies are probably resistant mutants that grow out in the presence of the phage. Or they could be a low level of contaminants in your phage stock (but less likely).
I suspect if you had removed the plates from the incubator a few hours earlier then you would not have seen those colonies.
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