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

Question 5

Where are endo toxins located

Answer 5

• On the outer membrane of GRAM NEGATIVE cell wall.

Question 6

How do endotoxins work

Answer 6

• They are released when the cell lyse and have an effect of the site of bacterial infection

Question 7

What is an example of an exotoxins, and what pathogenic effects does it cause

Answer 7

• Salmonella SPP
• Effects include fever, abdominal pain and diarrhoea

Question 8

How are exotoxins produced ?

Answer 8

• Soluble proteins produced and released into the body as bacteria metabolise in the host cell

Question 9

What kind of bacteria produces exotoxins?

Answer 9

• Both gram positive and gram negative produce exo toxins

Question 10

What is the named example for bacteria which produces exo toxins and what are the pathogenic effects ?

Answer 10

• Staphylococcus Aureus
• Food poisoning,
• Damage of cell membranes which cause internal bleeding

Question 11

What are two differences between ExoToxins and EndoToxins

Answer 11

• Endotoxins released from gram negative bacteria only where as exotoxins released from gram neg and pos.
• Endotoxins are polysaccharides whereas exotoxins are proteins

Question 12

Give one difference between the structure of Gram negative bacteria and Gram positive
bacteria

Answer 12

• Gram negative have a outer membrane lipopolysaccharide layer