Crystal violet stain is too light — colonies hard to see (Colony Formation Assay)

Question

Accepted Answer

Stained dish shows only very faint purple; colonies are hard to distinguish from background. Common causes: 1) Staining time was too short 2) Crystal violet stock was too dilute or expired 3) Washing was too aggressive and removed stain Solutions: 1) Extend staining time (20 – 30 min in 0.1 % crystal violet) 2) Use freshly prepared 0.1 % crystal violet 3) Wash gently with tap water 2 – 3 times only