Sometimes a Gram stain performed on histologic section will show a dark (blue, black) color.
Situation: Gram stain performed on histologic section shows a blue-black background with nuclei of cells showing a similar color.
Cause of the problem:
(1) under-decolorization with decolorizer (acetone, alcohol, other solvent) after the crystal violet stage
(2) crystal violet dried on the slide and become insoluble
The investigation needs to determine where the problem arose - technologist, reagents, and/or protocol.
Solutions:
(1) If under-decolorization was the likely problem:
(1a) increase the time for decolorization (or adhere to time if previously cut short)
(1b) use a faster acting solvent (undiluted if previously diluted)
(1c) replace the solvent
(2) Do not let the slides dry during the staining process. If blotting is performed before decolorization, then a damp paper or sponge should be used to reduce the risk of drying out.
