Gram stain separates most bacteria into gram-positive bacteria and gram-negative bacteria. Which of the following stain is NOT used in gram staining?
Correct Answer: Methylene blue
Description: The Gram stain involves the following four-step procedure: The crystal violet dye stains all cells blue/purple. The iodine solution (a mordant) is added to form a crystal violet-iodine complex; all cells continue to appear blue. The organic solvent, such as acetone or ethanol, extracts the blue dye complex from the lipid-rich, thin-walled gram-negative bacteria to a greater degree than from the lipid-poor, thick-walled gram-positive bacteria. The gram-negative organisms appear colorless; the gram-positive bacteria remain blue. The red dye safranin stains the decolorized gram-negative cells red/pink; the gram-positive bacteria remain blue. Ref: Levinson W. (2012). Chapter 2. Structure of Bacterial Cells. In W. Levinson (Ed), Review of Medical Microbiology & Immunology, 12e.
Category:
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