Questions and Answers
What is the defining characteristic of gram-positive bacteria in the Gram stain test?
They retain the crystal violet stain
What happens to the crystal violet stain in gram-negative bacteria during the Gram stain test?
It is washed away during the decolorization stage
What is the role of peptidoglycan in the Gram stain test?
It retains the crystal violet stain in gram-positive bacteria
What effect does alcohol have on gram-negative bacteria during the Gram stain test?
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Why do gram-negative bacteria take up the safranin counterstain in the Gram stain test?
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Study Notes
Gram Stain Test Characteristics
- The defining characteristic of gram-positive bacteria in the Gram stain test is the retention of crystal violet stain, which turns them purple.
- In gram-negative bacteria, the crystal violet stain is decolorized, meaning it is removed, during the Gram stain test.
Peptidoglycan and its Role
- Peptidoglycan, a thick multilayered peptidoglycan wall, is present in gram-positive bacteria, allowing them to retain the crystal violet stain.
Effects of Alcohol and Safranin Counterstain
- Alcohol decolorizes gram-negative bacteria, allowing the safranin counterstain to take its place and turn them pink.
- Gram-negative bacteria take up the safranin counterstain because they have been decolorized by the alcohol and do not retain the crystal violet stain.
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