Gram Staining

Richard Coico1

1 CUNY Medical School, New York, New York
Publication Name:  Current Protocols in Immunology
Unit Number:  Appendix 3O
DOI:  10.1002/0471142735.ima03os23
Online Posting Date:  May, 2001
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Abstract

Named after Hans Christian Gram who developed the method in 1884, the Gram stain allows one to distinguish between Gram‐positive and Gram‐negative bacteria on the basis of differential staining with a crystal violet‐iodine complex and a safranin counterstain. The cell walls of Gram‐positive organisms retain this complex after treatment with alcohol and appear purple, whereas gram‐negative organisms decolorize following such treatment and appear pink. The method described here is useful for assessing bacterial contamination of tissue culture samples or for examining the Gram stain status and morphological features of bacteria isolated from mixed or isolated bacterial cultures.

     
 
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Table of Contents

  • Reagents and Solutions
     
 
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Materials

Basic Protocol 1:

  Materials
  • Sample to be stained
  • recipeCrystal violet solution (see recipe)
  • recipeGram's iodine solution (see recipe)
  • recipeDecolorizing solution (see recipe)
  • recipeCounterstain (see recipe)
  • Inoculating loop (e.g., Fisher)
  • Glass slides
  • Bibulous paper (optional)
  • Microscope with oil immersion objective
NOTE: A Gram stain kit (e.g., Fisher) may be used in lieu of the staining reagents in the Materials list.
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Literature Cited

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