quiz on staining Flashcards
what is the gram positive control?
Staphylococcus epidermidis
what is the gram negative control?
Escherichia coli
cell morphology of Streptococcus thermophilus
coccus
cell morphology of Lactobacillus bulgaricus
rod
gram characteristic of Streptococcus thermophilus
gram (+), aciduric, thermophiles
gram characteristic of Lactobacillus bulgaricus
gram (+), acidophilic, thermophiles
what happens once the dye
penetrates the cell?
it will form bonds w/ intracellular materials and resist being washed away
what is a smear? what is the purpose? does this kill the bacteria?
first step in staining
purpose: to spread them in a thin layer on a glass slide
No
what are the 2 methods that kills the cells and fixes them to the slide?
heat fixation + methanol fixation
what are the advantages of using heat fixation rather than methanol fixation? 2 total
requires no chemicals and does not produce hazardous waste
what are the advantages of using methanol fixation as opposed to heat fixation? specify the type of culture for which this method is most advantageous.
produces fewer distortions of the cells, resulting in better results upon
staining, particularly when working w/ broth cultures
what are the different categories of staining?
Simple stains, Differential stains, Structural stains
1) how many stains are used in simple staining?
2) Give 2 examples of common basic dyes used in microbiology.
3) What type of cellular features can (+)/(-) dyes help visualize?
1) a single stain
2) Crystal violet and safranin
3) shape and size
for simple staining, what is the difference between the cation dye vs the anionic/acidic (-) dye in terms of procedure?
In a (-) stain, the stained slide is not washed
In a (+) stain, excess dye is usually rinsed off
describe how positive staining works. negative staining?
Positive staining (basic dyes): The (+) charged dye binds to the (-) charged cell surface + biomolecules inside the cell, staining the entire cell
Negative staining (acidic dyes): The (-) charged dye is repelled by the (-) charged cell surface, so it stains the background instead, leaving the cells as clear, unstained shapes
1) how many stains are used in differential staining?
2) Name 2 examples of differential stains
3) What is the main cellular structure that differential stains target?
4) differential staining distinguishes between what type of bacterial types?
1) 2
2) Gram stain and the acid-fast stain
3) cell wall
4) gram negative and gram positive
1) how many stains are used in structural staining?
2) Name 3 examples of structural stains.
3) What dye is commonly used in the endospore stain?
4) What is the purpose of structural stains?
1) 2
2) endospore stain, capsule stain, flagellar stain
3) Malachite green
4) to identify the presence or absence of a particular cell structure
what is THE most common problem w/ bacterial staining?
having a smear that is too thick
When spreading the cells, avoid making exclusively BLANK motions. Instead, opt of BLANK motions.
circular; side-to-side
is peptidoglycan an impervious layer? is it porous and allows passage of small molecules?
NO; YES
What is the primary stain in differential staining ? what is the mordant and its purpose?
crystal violet, a deep blue/purple
Gram’s iodine: helps the crystal violet dye bind more tightly to the bacterial cell wall
what does a decolorizer do to the cell wall?
what mixture is used in the lab for the decolorized?
what does the success of the gram staining technique depend on?
makes lipids soluble (dissolves outer mem lipids) and acts a dehydrating agent (for gram + to retain the dye)
alcohol and acetone
the decolorization step
why is the success of the gram staining technique depend on decolorization?
which type of cell loses their color, which retains their color?
why do you need to rinse the slide?
to see only gram positive bacteria
Gram-negative cells lose their color,
Gram-positive cells retain their color,
to stop the decolorization process, preventing over-decolorization
what is the purpose of counterstaining?
what are the commonly used counterstains? 2 total
what color will a gram (+) bacteria stain? gram (-)?
to color the Gram (-) bacteria that have become colorless after the decolorization step
Basic fuchsin and safranin
gram (+) = blue/purple
gram(-) = pink/light red
