Micro Lab Test 2 – Flashcards
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P. 181-184
Bacterial Morphology & arrangement
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EX.
Morphology- Coccus
Arrangement- Staphylococcus
Morphology- Bacillus
Arrangement- Streptobacillus
Morphology- Coccus
Arrangement- Diplococcus
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Round like grapes
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Cocci
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Little sticks or rods
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Bacillus
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P.194 #2
Eosin is a red stain and methylene blue is blue. What should be the result of staining a bacterial smear with a mixture of eosin and methylene blue?
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*Eosin is acidic & acts as a negative stain
*Methylene blue is basic
The smears background would turn out red while the cells would turn out blue.
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P.202 #1
Predict the effect on Gram-positive & Gram-negative cells of the following "mistakes" made when performing a Gram stain. Consider each mistake independently.
A. Failure to add the iodine.
B. Failure to apply the decolorizer.
C. Failure to apply the safranin.
D. Reversal of crystal violet and safranin stains.
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A. Everything will appear gram negative
B. Everything will appear gram positive
C. Gram (+) will be purple, gram (-) will be colorless
D. Wouldn't be able to read and would have to toss it.
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P. 202 #2
Both crystal violet and safranin are basic stains and may be used to do simple stains on Gram-positive and Gram-negative cells. This being the case, explain how they end up staining Gram-positive and Gram-negative cells differently in the Gram stain.
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It is the ability of gram positive cells to retain the crystal violet when subjected to alcohol decolorization. This ability is enhanced with the use of the mordant iodine.
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P.202 #3 (similar to one question on test)
If you saw large eukaryotic cells in the preparation made from your gumline, they were most likely your own epithelial cells. Are you gram positive or gram negative?
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Normal people are gram negative. It is the thick peptidoglycan of gram positive walls that makes them able to retain the crystal violet during decolorization. In fact, most cells, prokaryotic and eukaryotic are gram negative.
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P.210 #1
How does heating the bacterial smear during a ZN stain promote entry of carbolfuchsin into the acid-fast cell wall?
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Heating melts the mycolic acid and allows the stain to penetrate the cell walls.
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P.210 #3
Why do you suppose the acid-fast stain is not as widely used as the Gram stain? When is it more useful than the Gram stain?
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Very few bacteria are acid fast positive, so the test is less useful than a gram stain, which separates organisms into two large groups.
-Acid fast is useful when acid fast positive bacteria are suspected.
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P.220 #1
Why does this exercise call for an older (5-day) culture of Bacillus?
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Older bacteria are under greater nutritional stress so there will be more endospores present and able to visualize.
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Chromogen
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Color complex
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Chromophore
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Colored part
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Auxochrome
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Charged part
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3 reasons to heat fix?
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-Adheres the sample to the slide
-Kills bacteria
-Coagulates proteins
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3 things we see from a simple stain?
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-Size
-Shape
-Arrangement
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(T/F Question)
What are the 3 differential stains?
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Gram stains
Endospore stains
Acid-Fast stains
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Basic stains are ...
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Positively charged
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Acidic stains are ...
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Negatively charged
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Thick layer of PDG
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Gram-positive
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Think layer of PDG
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Gram-negative
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-Small rods
Random distribution
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Gram-negative
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-Small cocci tetrads
-Small cocci random
-Large streptobacillius
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Gram-positive
