Dirty background or uneven crystal violet staining (Colony Formation Assay)

Question

Accepted Answer

Staining shows blotches, smears, or uneven intensity across the dish — technical artifacts can be mistaken for real biological differences. Common causes: 1) Fixation time was too short or uneven 2) Crystal violet was not washed adequately (or was over-washed) 3) Dishes dried unevenly 4) Different staining conditions across replicate dishes Solutions: 1) Fix all dishes for the same time with the same fixative 2) Use the same crystal violet concentration and incubation time 3) Wash gently with tap water until background clears — same number of washes for every dish 4) Air-dry on a flat surface to avoid pooling