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18 Cards in this Set

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