Gram staining

Gram staining is a method for staining samples of bacteria that
differentiates between the two main types of bacterial cell wall.

It is named after the inventor, the Danish scientist Hans Christian Gram
(1853-1928), who developed the technique in 1884 to discriminate between
pneumococci and Klebsiella pneumoniae bacteria.

Gram Staining a Step by Step Procedure

  1. Heat fix the specimen.
  2. Add a basic dye to stain the sample. Crystal violet or gentian violet
     are suitable. Allow to stain for 1 minute. The slide should look violet
     in colour.
  3. Rinse off with water.
  4. Add iodine solution (1% iodine, 2% potassium iodide in water]]) for 1
     minute. This acts as a mordant and fixes the dye.
  5. Rinse with water.
  6. Apply 95% ethanol or a mixture of acetone and alcohol several times
     until no more colour appears to come from the sample.This leaves
     Gram-positive organisms stained purple and Gram-negative organisms
     unstained.
  7. Rinse with water.
  8. Apply a suitable counterstain. Opinions vary as to the best choice but
     suitable stains include safranin or fuchsin.This stains the gram
     negative organisms.
  9. Blot gently and allow to dry. Do not smear.

Results:

Inspect the slide under a microscope

     Gram positive organisms will appear blue-black or purple.
     Gram negative organisms will appear red.

Gram-positive bacteria have a thick meshlike cell wall made of peptidoglycan
which is capable of retaining the violet dye. Gram negative bacteria have a
thin cell wall made of a layer of peptidoglycan surrounded by an outer
membrane containing lipids.

As a rule of thumb (which has exceptions), Gram-negative bacteria are more
dangerous as disease organisms, because their outer membrane acts as
"camouflage"; the human body does not contain peptidoglycan and in fact
produces an enzyme called lysozyme which attacks the open peptidoglycan
layer of Gram-positive bacteria. Gram-positive bacteria are also much more
susceptible to penicillin.

   * Gram-positive bacteria
   * Gram-negative bacteria

How to - Physics - History - Companies - Internet - Video Games - List of Phobias - September 11, 2001
Radio - Timelines - Chemistry - Genealogy - Family - Film - SARS - Cancer - Medicine - DVD - Calendar
Countries - Disease - Health Science - Dentistry - Economics - AIDS - Law - Autism - Statistics - Bible
Recipes - Architecture - Computers - History of the Internet - Personal computer - Apple Macintosh
War - Presidents of the United States - United States Constitution - Universe - Philosophy - Animals
Biology - United States Constitution - Marketing Topics - Sports - Television - History of Computing

Mortgages - Mobile Phones - Car Credit - Wedding rings - Art Prints