Bacterial Pathogenesis (L24-25)

Question 1

List the sources of pathogen infection.

4

Answer 1

• Environmental
• Zoonotic
• Normal Human microbiota
• Another infected host

Question 2

List the factors that influence pathogenic transmission.

3

Answer 2

• Infective dose
• Stability outside the host
• Host susceptibility

Question 3

List the factors controlling the growth of pathogens.

4

Answer 3

• Nutrient availability in host
• Physical environment in host
• Normal microbiota
• Host defences

Question 4

Define Virulence.

Answer 4

A quantitative measure of the pathogenicity of an organism.

ie. the relative ability of a pathogen to cause disease.

Question 5

What are virulence factors?

Answer 5

Molecules (often proteins) that enable a microorganism to establish itself on or within a host of a particular species and enhance its potential to cause disease. Bacteria can convert from avirulent (non-disease causing) strain to virulent strain by obtaining DNA that encodes specific virulence factor(s).

Question 6

Name the first step in pathogenesis.

Answer 6

Adhesion.

Question 7

What is an adhesin?

Answer 7

A specific molecule on the bacterial surface. Usually a surface carbohydrate binding protein (eg. lectin). The adhesin binds a specific receptor to adhere to the cell surface.

Question 8

What are Bacterial Fimbriae or Pili?

Answer 8

Specialized, multimeric, ‘appendages’ protruding several microns - much further than individual surface proteins. Used by bacteria to adhere to one another and to animal cells - often first step in infection. Adhesin is often present at the tip of the fimbriae.

Question 9

List the routes of pathogenic invasion.

4

Answer 9

• Direct access via wounds, bites, burns etc
• Access via colonised surfaces
• Transport by phagocytes at surfaces
• Invading normally non-phagocytic epithelial cells

Question 10

_____ are responsible for much of the direct damage caused by bacterial pathogens.

Answer 10

Toxins.

Question 11

Name the most common endotoxin.

What effect does it have on the host?

Answer 11

Lipopolysaccharide (LPS).

LPS is recognised by innate immune system and elicits a variety of inflammatory responses that can result in ‘septic shock’ (endotoxic shock).

Question 12

List the types of exotoxin.

3

Answer 12

• Toxins with enzymatic activity (AB toxins)
• Superantigens
• Pore-forming toxins

Question 13

Give 3 examples of AB exotoxins.

Answer 13

• Botulinum toxin
• Diphtheria toxin
• Antrax toxin

Question 14

Give 2 examples of Pore-forming exotoxins.

Answer 14

• Staphylococcus aureus α-toxin
• Streptococcus pyogenes SLO
  (streptolysin O)

Question 15

Name the types of direct damage pathogens can inflict on the host.
(2)

Answer 15

• Bacterial toxins

- Degradative enzymes