Microbial Pathology

Question 1

What are the five pathogens described in this lecture?

Answer 1

Viruses, Fungi (eukaryotes), Protozoa (eukaryotes), Helminths (eukaryotes), Bacteria (bacteria)

Question 2

What are Koch’s Postulates?

Answer 2

Guidelines used to demonstrate that a specific pathogen causes specific disease symptoms
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 causes the same disease when injected into a healthy host
4. The microorganism can be recovered from the experimentally infected host.

Question 3

What are the exceptions to Koch’s Postulates

Answer 3

• Microbes that can’t be cultured (ie. Treponema pallidium)
• Pathogens that also can be found in healthy subjects (ie. Vibro cholera)

Question 4

What are they key stages of Microbial Pathogenesis?

Answer 4

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

Question 5

What are the bacterial virulence factors?

Answer 5

1. Adherence to host cells
   
   • Adhesions such as fimbriae (bind to host cells) eg. Neisseria gonorrhoeae
2. Invasion of host tissues
   
   • Modality (move through mucus) eg. helicobacter pylori (flagella)
   • Internalin-related proteins (InIB) eg. Listeria monocytogenes
3. Replication within host tissues
   
   • Siderophores (bind iron) Yersinia pestis eg. the siderophore Yersiniabactin solubilises metal bound to host proteins and transports it back to the bacteria
   • Capsules (resist phagocytosis) eg. Streptococcus pneumoniae
4. Disease causing damage to host tissues (Pathology)
   
   • Endotoxins: cause inflammation
   • Exotoxins: can be fatal

Question 6

Describe endotoxins

Answer 6

Endotoxins are Lipopolysaccharides (LPS) components found in the outer membrane of Gram-negative bacteria, and elicit strong immune responses.
When bacteria are destroyed, they release LPS. It is not the endotoxin that causes the disease, but the body’s immune system because it goes into an overworked state.

Potential effects of Endotoxin Lipid A:
Fever, inflammation, blood clotting, shock

Question 7

Describe exotoxins

Answer 7

Exotoxins are proteins produced within living bacteria, and then released into the surrounding medium. There are three types:
- Cytotoxins: The cytotoxin (Streptolysin) produced by the bacteria Streptococcus pyogenes causes the complete lysis of red blood cells (Beta Haemolysis)
- Neurotoxins: The neurotoxin (Botulinum) produced by the bacteria Clostridium botulinum causes paralysis
- Enterotoxins: The enterotoxin (Shiga toxin) produced by the bacteria Shigella dysenteriae causes severe dysentery (lysis of the gut and bloody diarrhea