6.2 Bacteria as pathogens

Question 1

Describe the structure of gram positive bacteria

Answer 1

• Thick layer of peptidoglycan
• Techoic acid trapped in layer of peptidoglycan layer

Question 1

Spec Points

Answer 1

Understand that bacteria can be agents of infection, invading and destroying
host tissues and producing toxins.
ii Understand that pathogenic effects can be produced by exotoxins
(Staphylococcus spp.), endotoxins (Salmonella spp.) and invasion of host
tissue (Mycobacterium tuberculosis).

Question 2

Describe the structure of gram negative bacteria

Answer 2

• Thin layer of peptidoglycan between two membranes
• No techoic acid
• Layer of lipopolysaccharides on outer membrane

Question 3

Describe the process of gram staining

Answer 3

• Add purple crystal violet/ iodine complex to stain
• Add alcohol to decolourise
• Add safranin to counterstain

Question 4

What are the two kinds of toxins

Answer 4

• Endo toxins
• Exo toxins