Principle gram staining?

Question

GRAM STAINING

Answer 1

Here you find illustrated description of method, history and mechanism etc:

http://www.uphs.upenn.edu/bugdrug/antibi...

http://en.wikipedia.org/wiki/Gram_stain

Answer 2

on the basis of gram staining bacteria r of 2 types

1)gram +

2)gram -

Principle

Bacteria are stained with cristal violet which turns all the bacteria bluish purple.

then KI solution is added for which the stain will be fixed due to formation of a complex

The in yhe next step we destain the complex with water and alcohol

If the stain comes out then the bacteria we used  is gram-

else the bacteria is gram+

In the cellwall of gram+, both horizontal and vertical peptide linkage are present , due to which mesh is dense and here the stain doesn't come out.

But in gram- bacteria  either horizontal or vertical peptide linkage are present for which mesh are loose and hence stain comes out

Answer 3

Principle of Gram's Stain

The crystal violet stain is the primary stain, which stains everything in the smear blue. The Gram's iodine acts as a mordant that causes the crystal violet to penetrate and adhere to the gram-positive organisms. The acetone-alcohol mixture acts as the decolorizer that washes the stain away from everything in the smear except the gram-positive organisms. The safranine is the counter-stain that stains everything in the smear that has been decolorized: pus cells, mucus, gram-negative organisms. The gram-negative organisms will stain a much deeper pink than the pus cells, and mucus will stain even lighter pink than the pus cells.

Answer 4

principle is as elabotated by richa. is very much currect. so i will say only theis fram stains are only used to define the gram positive and negative bacteria for the research uses.

Answer 5

Gram staining is used to distinguish between different bacteria. The stain (crystal violet) specifically targets a cell wall component called peptidoglycan (http://en.wikipedia.org/wiki/Peptidoglyc...

Gram positive cells have a thick layer of peptidoglycan in their cell walls, and will thus take up more of the stain and appear dark. Gram negative cells have less peptidoglycan, and will thus take up less of the stain and will not appear dark.

Answer 6

Staining deviced by Christian Gram. Bacteria treated with crystal violet and Iodine. All bacteria attain purple colour. Then washed with alcohol. Those bacteria which retain original purple color are gram positive and those from which colour is lost is gram negative. This is due to Peptidoglycan cell wall

Answer 7

Gram staining (or Gram's method) is an empirical method of differentiating bacterial species into two large groups (Gram-positive and Gram-negative) based on the chemical and physical properties of their cell walls.[1]

The method is named after its inventor, the Danish scientist Hans Christian Gram (1853 – 1938), who developed the technique in 1884 to discriminate between pneumococci and Klebsiella pneumoniae bacteria.[2]

Gram-positive bacteria have a thick mesh-like cell wall made of peptidoglycan (50-90% of cell wall), which stain purple and Gram-negative bacteria have a thinner layer (10% of cell wall), which stain pink. Gram-negative bacteria also have an additional outer membrane which contains lipids, and is separated from the cell wall by the periplasmic space. There are four basic steps of the Gram stain, which include applying a primary stain (crystal violet) to a heat-fixed smear of a bacterial culture, followed by the addition of a mordant (Gram's iodine), rapid decolorization with alcohol or acetone, and counterstaining with safranin or basic fuchsin.

Crystal violet (CV) dissociates in aqueous solutions into CV+ and chloride (Cl – ) ions. These ions penetrate through the cell wall and cell membrane of both Gram-positive and Gram-negative cells. The CV+ ion interacts with negatively charged components of bacterial cells and stains the cells purple. Iodine (I – or I3 – ) interacts with CV+ and forms large complexes of crystal violet and iodine (CV – I) within the inner and outer layers of the cell. When a decolorizer such as alcohol or acetone is added, it interacts with the lipids of the cell membrane. A Gram-negative cell will lose its outer membrane and the peptidoglycan layer is left exposed. The CV – I complexes are washed from the Gram-negative cell along with the outer membrane. In contrast, a Gram-positive cell becomes dehydrated from an ethanol treatment. The large CV – I complexes become trapped within the Gram-positive cell due to the multilayered nature of its peptidoglycan. The decolorization step is critical and must be timed correctly; the crystal violet stain will be removed from both Gram-positive and negative cells if the decolorizing agent is left on too long (a matter of seconds).

After decolorization, the Gram-positive cell remains purple and the Gram-negative cell loses its purple color. Counterstain, which is usually positively-charged safranin or basic fuchsin, is applied last to give decolorized Gram-negative bacteria a pink or red color.[7][8]

Some bacteria, after staining with the Gram stain, yield a Gram-variable pattern: a mix of pink and purple cells are seen. The genera Actinomyces, Arthobacter, Corynebacterium, Mycobacterium, and Propionibacterium have cell walls particularly sensitive to breakage during cell division, resulting in Gram-negative staining of these Gram-positive cells. In cultures of Bacillus, Butyrivibrio, and Clostridium a decrease in peptidoglycan thickness during growth coincides with an increase in the number of cells that stain Gram-negative[9] In addition, in all bacteria stained using the Gram stain, the age of the culture may influence the results of the stain.

Answer 8

The staining technique is based on the difference between the cell wall composition of different bactweria.

Bacterial cell wall may have higher lipid content or the protein content.

Also the stains used in Gram staining have different affinity for these components and they bind with them reversibly or irreversibly.

Hence Gram positive bacteria bind the stain irreversibly and can not be decolourised by alcohol also where as Gram negative bacteris bind the stain reversibly and give it away when washed with water and alcohol.  Then they take up the secondary stain become pink stained.

The difference in cell wall composition and affinity of stain to different cell walls is the principle.

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