Microorganism Stains Flashcards
(32 cards)
What is the Giemsa stain most commonly used in the histology laboratory?
The May-Grunwald Giemsa.
What does the May-Grunwald Giemsa stain?
Hematopoietic (blood) cells and microorganisms. Malaria is pictured.
True or False: The May-Grunwald Giemsa is a progressive stain.
False. The May-Grunwald Giemsa stain is regressive in 2 ways. It differentiates with both acetic acid and alcohol.
True or False: The May-Grunwald Giemsa stain can be used to demonstrate h. Pylori.
Very true. Before IHC staining for h. Pylori became available, the Giemsa was the most commonly used stain for helicobacter. Not because it was the best, but because it was relatively quick and easy.
How thick should sections be cut for the Giemsa Stain?
Lymph nodes and bone marrow should be cut at least at 3 microns, otherwise 4 microns.
Does a Diff-Quik stain bacteria?
Yes. It is commonly used for h.pylori.
What does a Gram stain demonstrate?
Gram positive and Gram negative bacteria. They can both be various shapes.
In the Gram stain, what so-called mordant creates the dye lake with Crystal Violet?
Iodine.
What happens to bacteria in a Gram stain when you decolorize?
The peptidoglycans in the cell wall of bacteria shrink and tighten to trap the crystal violet-iodine dye lake, but the cell walls of Gram negative bacteria don’t have as many peptidoglycans and get decolorized.
What can you use to decolorize a Gram stain?
Either alcohol or acetone.
The most important stain in microbiology is the Gram stain. Why is it called a differential stain?
It differentiates between Gram positive and Gram negative bacteria.
True or False: Gram positive bacteria stain only with Crystal Violet and Gram negative bacteria stain with either Basic Fuchsin or Safronin.
False. They both stain with both. Crystal Violet get decolorized from Gram negative bacteria and you can’t see the Basic Fuchsin or Safronin in Gram positive bacteria because the Crystal Violet is so dark.
What is the counterstain for a Gram stain?
Picric Acid.
Can all bacteria be classified as Gram negative or Gram positive?
No. You can’t differentiate using a Gram stain if there is no cell wall as in m. Tuberculosis, Chlamydia and Rickettsia.
What happens if you spend too long in the decolorizer while doing a Gram stain?
You get no Crystal Violet staining.
What is an argyrophilic silver stain?
A silver stain that needs a separate reducer. Grocott’s Methenamine Silver is pictured with Aspergillus fungus.
What oxidizer has replaced Chromic Acid in the GMS stain?
Periodic Acid. GMS with PCP pictured. (Pneumocystis carinii) pnuemonia.
How does the GMS stain work?
In methenamine silver stains, once polysaccharides in fungal cell walls are oxidized to aldehydes, slides are placed in the methenamine silver solution and heated. The silver binds with the aldehydes, and because methenamine breaks down to formaldehyde and ammonia, the silver is reduced by the formaldehyde in the same step. Then, the section is toned, unreduced silver is removed, and a counterstain is applied.
Why is chromic acid the preferred oxidizer for a GMS?
It is a strong oxidizer and gives less background staining.
What control should be used for the GMS?
If possible, the same organism that you are staining for. If not the exact same organism, it should at least be the same size.
Why do you need organisms of the same size as a control for the GMS?
Smaller organisms take longer to develop.
True or False: If, when doing the GMS, the cell wall of a fungus has turned paper bag brown, but the inside of the cell is still light, you should leave it longer in the silver.
False. Remove it from the silver, rinse, and tone it. The cell wall should now be black, and the interior of the cell light gray and visible. This is a correctly stained GMS.
True or False: You should not use metal forceps with silver stains.
True. At least not unless they are coated, because they will react with the silver.
What is the difference between an overdeveloped and an overtoned GMS.
Overdeveloped would show the organism colored solid black with the interior of the cell not visible. Overtoned would show a purple-brown sepia color to the organism.
