2.1 Flashcards
Gram staining consists of 4 steps: What are they
1) Primary staining with crystal violet
2)Application of a mordant to bind the dye
3)Rinse with a decolorizing agent to release unbound dye
4)Counterstaining with safranin
Bacteria containing a lipid layer will
not bind the crystal violet dye, and will be counterstained
Gram-positive bacteria retain
crystal violet and will be Purple
Gram-negative bacteria will be counterstained with
safranin and will be Pink
Negative staining is used to study bacteria that are
difficult to stain or cannot be heat fixed.
What does the negative staining stain?
The background so it can be more easily seen
What is used for negative stain
India Ink or Nigrosin are used. They are acidic stains
Since the surface of most bacterial cells is negatively charged (what happens in negative staining)
the cell surface repels the stain, but the glass does not.
what is acid-fast staining used to stain
Mycobacterium
In acid-fast staining, heat allows carbol fuchsin stain to pass
through the waxy mycolic acid in the cell wall.
Once removed from heat, an acid alcohol decolorizer is applied. The stain will be released from all bacteria EXCEPT Mycobacterium
Other cells can then be counterstained with methylene blue or another simple stain
What are bacterial endospores
A dormant state some bacteria can produce under highly unfavorable conditions
Malachite green and heat are used to
drive stain into endospores so that it does not wash out.
Counterstain of safranin stains the vegetative cells______ to provide contrast in endospore staining
pink
