Differentiate gram negative from gram positive bacteria?

about gram staining,

Differentiate gram negative from gram positive bacteria?
Gram staining (or the 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.





Gram-negative bacteria are more dangerous as disease organisms, because their outer membrane is often hidden by a capsule or slime layer which hides the antigens of the cell and so acts as "camouflage"


Gram-negative bacteria have lipopolysaccharide in their outer membrane, an endotoxin which increases the severity of inflammation.








Gram-positive infections are generally less severe because the human body does not contain peptidoglycan; in fact, the human body produces an enzyme called lysozyme that attacks the open peptidoglycan layer of Gram-positive bacteria. Gram-positive bacteria are also frequently much more susceptible to beta-lactam antibiotics, such as penicillin.











Although Gram-positive bacteria have a thick mesh-like cell wall made of peptidoglycan and Gram-negative bacteria have a thinner layer, this is not the basis for the difference between these bacteria in their ability to retain crystal violet. Furthermore, Gram-negative bacteria have an additional outer membrane which contains lipids, and is separated from the cell wall by the periplasmic space. Neither does this explain the differences in terms of Gram stain. The mechanism for the difference curiously remains unknown.
Reply:Basically, bacteria have different amounts of a substance called peptidoglycan in their cell walls.





Gram + bacteria have a thick cell wall with lots of peptidoglycan, and gram - bacteria have a very little amount of peptidoglycan covered by a layer of lipids .





When you do a gram stain, the thick cell wall of gram + bacteria traps the violet dye inside the cell wall, giving them a coloured appearance. At the same time, the lipids on the gram - bacteria dissolve, so that the peptidoglycan is on the outside.





After this you wash the slide with alcohol. The alcohol washes the dye off the gram - bacteria, but since the dye is trapped inside the thick cell wall of the gram + bacteria, they retain the colour, but the gram - bacteria do not.

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