You have made a smear of a bacterial culture and have performed the Gram stain on it. Looking at the organism under the microscope, you notice that the cells do not seem to be the dark blue-purple of a gram-positive reaction, but instead are light purple. Your staining procedure was performed correctly. What is your best explanation as to why the bacteria have stained this way?
A. The specimen did not undergo heat fixation before staining; therefore, the primary dye does not stick properly to the wall.
B. These are mutant bacteria which cannot be stained like other bacteria.
C. The bacteria were taken from an inappropriate medium, and a chemical is interfering with proper staining of the cells.
D. There is something in the wall of the bacteria that has affected the uptake of the crystal violet into the cell wall, thereby staining it improperly.
Answer: D
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