The Gram-staining procedure is best described as which of the following?

• A. A selective culture technique used to isolate specific bacterial species
• B. A biochemical test to detect the presence of endospores in bacteria
• C. A simple staining method that uses only one dye to color all bacterial cells
• D. A differential staining technique that distinguishes bacteria based on cell wall composition

Answer: (D)

Verified step by step guidance

1. Understand that Gram staining is a method used to differentiate bacteria into two major groups: Gram-positive and Gram-negative, based on differences in their cell wall structure.
2. Recognize that the procedure involves multiple steps including application of a primary stain (crystal violet), a mordant (iodine), a decolorizer (alcohol or acetone), and a counterstain (safranin).
3. Know that Gram-positive bacteria retain the crystal violet stain due to their thick peptidoglycan layer, appearing purple under the microscope, while Gram-negative bacteria lose the crystal violet during decolorization and take up the counterstain, appearing pink or red.
4. Identify that this staining method is differential because it distinguishes bacteria by their cell wall composition rather than simply coloring all cells the same way.
5. Conclude that Gram staining is not a selective culture technique, a biochemical test for endospores, or a simple staining method, but a differential staining technique based on cell wall differences.