Gram postive and negative Flashcards Preview

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Flashcards in Gram postive and negative Deck (11):

What are gram negative and positive classified as ?

They are classified as bacteria .


Which bacteria cell is more susceptible to antibiotics and why ?

Gram positive are more susceptible to antibiotics because of the lack of outer membrane . Also they are rounded by a thick cell wall .

Many antibiotics are designed to attack the integrity of the cell wall therefore killing the cell .Absorbed the stain


What is the difference between Gram positive and negative ?

Gram positive bacteria appears purple in colour under the microscope .Whereas ,gram negative bacteria appears pink in colour .

- Outer membrane is present in gram positive and is absent in gram negative .

- Peptidoglycan layer is thick and multi-layered in gram positive whereas in gram negative is peptidoglycan layer is thin and single layered.

-Periplasmic space is absent in gram positive and is present in gram negative

- Cell wall is 20-30 nm in gram positive whereas cell wall is around 5- 10 nm

- Cell wall is smooth in gram positive and cell is wavy in gram negative

- Cell wall contains virtually noa lipopolysaccharide content in gram positive and cell wall high lipopolysaccharide content in gram negative .

- Lipid and lipoprotein content is low in the cell wall of gram positive and lipid and lipoprotein content is high in the cell wall is gram negative .

- More susceptible to antibiotic in gram positive and
is more resistant to antibiotics in gram negative

Mesosomes (increase surface area of plasma membrane )
- is less prominent in gram negative and is more prominent in gram positive bacteria .

Teichoic acids present in the cell wall of gram positive and absent in gram negative

Susceptibility to anoic detergents is high for gram positive and is low for gram negative

Toxins produced
- Primary endotoxins for gram negative
-Primary exotoxins for gram positive

-Examples for gram positive includes actobacillus and an example for gram negative includes aeetobacter .


What is the thick peptidoglycan responsible for ?

Is responsible for retaining the stain even after decolourization .


Why is gram negative harder to treat ?

This is because of the membrane present around the cell wall of gram negative bacteria increases risk of toxins to the host but this membrane is absent in gram positive bacteria .


Why are gram negative bacteria resistant to antibiotics ?

Because a cell wall with an outer membrane protects them from an antibiotics .


Why do gram positive purple ?

Because the thick peptigloycan wall absorbs the stain and they do not have a outer wall .


What does penicillin do ?

Its stops the synthesis of the cell wall on growing gram positive bacteria but it doesn't have the same effect on gram negative because it has a thinner cell wall and two lipid membranes .


During the staining process

Two stains are added to the bacterial smear a crystal violet and safrainin .

- If you see a purple stain when observing the smear under a microscope it means gram positive are present
- if the smear has a pink stain it indicated that gram negative is present


Why do we retain these colours ?

This is because their thinner cell walls and lipid membranes allow ethanol applied during the method to wash off all the crystal violet purple stain and to then retain the pink safransin stain


How is carried out ?

1. Applications of crystal violet
2. Applications of iodine mordant
3. Alcohol Wash decolourization
4. Applications of Safrainin.