L1: Bacterial Pathogenesis

Question 1

What were Koch’s postulates initially used as?

Answer 1

A set of rules for identifying a connection between a microbe and a disease.

Question 2

Define the term ‘microbiome’.

Answer 2

The entire microbial populations that exist and interact with a specific environment.

Question 3

Define the term ‘colonisation resistance’

Answer 3

The mechanism through which the intestinal microbiota defend themselves against foreign pathogens.

Question 4

Colonisation resistance can be direct or indirect. Explain this.

Answer 4

Direct - normal microbiota limit nutrient availability to stunt the growth of the pathogens.
Indirect - the microbiota activate the innate immune cells and release metabolic products.

Question 5

Define the term ‘serotype’.

Answer 5

Separate groups within a species of microbe that all have the same antigens on their surface.

Question 6

E.coli can be a commensal or a pathogen and so they have different serotypes. Give two examples.

Answer 6

E. coli K12 - commensal gut isolate.

E. coli O157/H7 - causes food poisoning/haemolytic uremia (EHEC).

Question 7

Since they are serotypes, what causes the disease difference?

Answer 7

The whole genome.

Question 8

Explain Pathogenicity Islands.

Answer 8

PAIs are a collection of genes that are clustered together on DNA and are inolvd in pathogenesis. Usually formed through horizontal gene transfer.

Question 9

Define the term ‘virulence factor’.

Answer 9

Bacterial product/strategy that contributes to the ability of the bacterium to survive in the host and cause infection.

Question 10

Give a description of the type 3 secretion system.

Answer 10

• Complex molecular ‘syringe’.
• System used by salmonella and EHEC.
• Injects proteins into the cells that can alter processes such as actin polymerisation.

Question 11

Explain how the cholera toxin, produced by Vibrio cholera, results in watery diarrhoea.

Answer 11

Increases adenylate cyclase activity, which increases cAMP levels, massive efflux of ions and water from enterocytes.

Question 12

Define the term ‘biotype’.

Answer 12

A group of organisms having an identical genetic constitution.

Question 13

How does host genetics affect cholera susceptibility?

Answer 13

It is a blood group dependent disease –> binds to blood group O extremely well.

Question 14

What does EHEC stand for?

Answer 14

EnteroHemorrhagic Escherichia Coli, E. coli O157 : H7.

Question 15

What toxin does EHEC produce? Effectsof this toxin?

Answer 15

Shiga toxin, which:

1. Modifies rRNA and inhibits translation.
2. Induces signalling pathways involved in cell apoptosis.
3. Haemolytic uremia.

Question 16

Additional VFs produced by EHEC?

Answer 16

Adhesins, mucinase and T3SS.

Question 17

The role of intimin in EHEC?

Answer 17

The protein is inserted into the enterocytes when EHEC attaches using its fimbriae. It is then presented on the host cell as a receptor for the bacterial adhesion Tir, forming a ‘lock and key’ interaction that allows the T3SS to introduce further effector molecules.

Question 18

How does EHEC induce tissue trophism?

Answer 18

The T3SS causes actin filaments to be rearranged.