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18 Cards in this Set
- Front
- Back
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What is the most important differential staining procedure used in microbiology?
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-gram stain
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What are differential stains?
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-staining that uses more than one dye and used to distinguish between different groups of bacteria
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Who developed the gram stain?
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-Danish physician, Hans Christian Gram in 1884
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What does gram reaction depend on?
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-structurally intact organisms
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Describe gram positive cells.
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-retain primary crystal violet dye when complexed with iodine
-appear purple-blue -thick walls with one layer and have a very high conc. of peptidoglycan -low lipid concentation |
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Describe a Gram negative cell.
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-unable to retain crystal violet-iodine complex when washed with alcohol
-retain Safranin and appear red -two or more cell wall layers, small amount of peptidoglycan -high lipid concentration |
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What is peptidoglycan?
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-found only in bacteria
-high molecular weight -has repeating carbohydrate polymer linked by AA bridges -forms backbone of cell wall |
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What occurs during decolorization?
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-alcohol removes lipids in cell walls causing them to become porous
-alcohol shrinks peptidoglycan (locking in dye in Gr +) |
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How old should cultures be before they should be discarded?
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-16 to 24 hours if possible
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How does acidity affect gram cell stain?
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-cells grown in acidic environments can lose their ability to retain the CV-I complex resulting on erroneous Gram reactions
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What happens in a flase Gram negative?
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-slide is overdecolorized and appear pink (though should be blue)
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What color do yeasts and fungi sometimes APPEAR to stain?
Animal cells? |
-blue
-red *Gram staining is only differential for bacteria! |
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What are the four basic cellular characteristics of a bacterium that should be described when identifying it?
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-Gram stain reaction
-Size -Shape -Spatial Arrangement |
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What is the substitute dye that can replace safranin for colorblind people?
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-Bismarck Brown
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What is a primary stain?
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-the initial stain used which enters both types of cells: crystal violet
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What is a mordant?
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-makes the staining solution work more intensely
-wherever it meets dye, it forms water insoluble pools (slightly soluble in alcohols and acetone) |
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Review problems with Gram staining.
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Appendix E, pg 27 and 28
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What are 6 things TA's look for to grade a stained slide?
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-cellular damage from heat fixing
-density -distribution -stain precipitation -Gram reaction -Quality of counterstain |
