You have made a smear of a bacterial culture and have performed the Gram stain o

Question

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. 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.

b. These are mutant bacteria which cannot be stained like other bacteria.

c. The specimen did not undergo heat fixation before staining; therefore, the primary dye does not stick properly to the wall.

d. The bacteria were taken from an inappropriate medium, and a chemical is interfering with proper staining of the cells.

Explanation / Answer

Ans:

(C) The specimen did not undergo heat fixation before staining; therefore, the primary dye does not stick properly to the wall.

Fixation is necessary to fix cells so that no internal or external reactions takes place. Also, fixed cells take up stain properly and stain dark.

But without fixation, cells are loosely bound and to not take up stain efficiently.

Other possible answer is (a).

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