Gram Stain

Question 1

What colour do Gram-positive bacteria stain?

Answer 1

Purple

Question 2

Name two examples of Gram-positive bacteria

Answer 2

Lactobacillus acidophilus

Staphylococcus aureas

Question 3

What colour do Gram-negative bacteria stain?

Answer 3

Pink

Question 4

Why do Gram-negatives stain pink?

Answer 4

They are decolourised by ethanol because they have only a thin layer of peptidoglycan in the cell wall, so can take up the counter stain (usually red safranin)

Question 5

Name an example of a Gram negative bacteria

Answer 5

Escherichia coli

Question 6

What is peptidoglycan made of?

Answer 6

Two sugars: N-acetylglucosamine and N-acetylmuramic acid, and some amino acids

Question 7

Name two examples of surface antigens found in Gram-positive bacteria

Answer 7

Teichoic acids and lipoteichoic acids

Question 8

What is the function of the teichoic/lipoteichoic acids?

Answer 8

Evoke an immune response

Bind important ions for transport into the cell

Question 9

What is the LPS

Answer 9

Lipopolysaccharide layer, an outer membrane in th cell wall of Gram-negative bacteria, contains periplasmic space which is rich in proteins, including enzymes to break down host cell components

Question 10

Purpose of porins in the LPS

Answer 10

Allow passive diffusion of small molecules into periplasmic space

Question 11

What is Braun’s lipoprotein

Answer 11

Lipoprotein that links the outer membrane to the peptidoglycan in gram-negative cell walls