Lecture 33

Question 1

Examples of important microbial pathogens

Answer 1

Protozoa - plasmodium spp. (malaria parasites)
Helminths - ancylostoma duodenale (hook worm)
Bacteria - bacillus anthracis (gram- positive, endospore-forming, rod-shaped bacterium)

Question 2

What are koch’s postulates?

Answer 2

guidelines used to demonstrate that a specific pathogen causes specific disease symptoms

Question 3

4 points of Koch’s postulates

Answer 3

1. The pathogen must be present in every individual with the disease
2. A sample of the microorganism taken from the diseased host can be grown in pure culture
3. A sample of the pure culture caused the same disease when injected into a healthy host
4. The microorganism can be recovered from the experiementally infected host

Question 4

Exceptions to Koch’s postulated

Answer 4

• microbes that can’t be cultures
• pathogens that also can be found in health subjects

Rewatch this lecture slide

Question 5

Key stages of microbial pathogenesis

Answer 5

1. Adherence to host cells
2. Invasion of host tissues
3. Replication within host tissues
4. Disease causing damage to host tissues (pathology)

Question 6

How bacterial virulence factors relate to the first stage (adherence to host cells) of microbial pathogenesis

Answer 6

Adherence to host cells
- adhesions such as fibrae (bind to host cells)

E.g: neisseria gonorrhoeae

Question 7

How bacterial virulence factors relate to the second stage (invasion of host cells) of microbial pathogenesis

Answer 7

• motility (move through mucus)
  E.g: helicobacter phylori (flagella)
• internalin-related proteins (InIB)
  E.g: listeria monocytogenes

Question 8

How bacterial virulence factors relate to the third stage (replication within host cells) of microbial pathogenesis

Answer 8

• siderophores (bind iron) - yersinia pestis e.g the siderophore Yersiniabactin solubilises metal bound to host proteins and transports it back to the bacteria
• capsules (resist phagocytosis) e.g streptococcus pneumoniae

Question 9

How bacterial virulence factors relate to the fourth stage (disease causing damage to host tissues (pathology)) of microbial pathogenesis

Answer 9

Endotoxins: cause inflammation
Exotoxins: can be fatal

(Toxic virulence factors)

Question 10

Endotoxins

Answer 10

• lipopolysaccarides (LPS) components found in the outer membrane of Gram-negative bacteria, and elicit strong immune responses

Question 11

Exotixins are..

Answer 11

Produced within living bacteria and then realised into the surrounding medium

Question 12

Three types of exotoxins

Answer 12

• cytotoxins
• neurotoxins
• entertoxins

Question 13

What are cytotoxins

Answer 13

The cytotoxin (streptiolysin - an extracellular enzyme) produced by the bacteria streptococcus pyrogens causes the complete lysis of red blood cells (beta haemolysis)

Question 14

Neurotoxins

Answer 14

The neurotoxin (botulinum) produced by the bacteria clostridium botulinum causes paralysis

Question 15

Enterotoxins

Answer 15

• the entrotoxins (shiga toxic) produces by the bacteria shigella dysenteriae causes severe dysentery