Vibrocholerae

Question 1

What is an outbreak?

Answer 1

• Occurence of disease in excess of what would normally be expected in a defined community, geographical area or season
• May extend several countries and may last few days, weeks, years

Question 2

What is an epidemic?

Answer 2

Widespread occurence of an infectious disease that spreads quickly at a particular time and affects many individuals in a community

Question 3

What is a pandemic?

Answer 3

An epidemic occurign worldwide or over a wide area crossing international boundaries and usually affecting a large number of people

Question 4

What is cholera?

Answer 4

• An acute diarrheal infection caused by ingestion of food or water, contaminated with bacterium Vibrio cholerae

Question 5

Why is the infection rate of cholera lower in food?

(2 marks)

Answer 5

Ingestion by water - 10³-10⁶

By food - 10²- 10⁴

• In food it is protected from acid and survives so decreases needed dose for infection

Question 6

What are the clinical symptoms of cholera?

(4 marks)

Answer 6

• Acute watery diarrhea
• Stools
• Vomiting
• Leg cramps - due to loss of water and salt in blood

Question 7

In what ‘medium’ does vibro cholera live in?

Answer 7

Water

Question 8

What are the main characteristics of vibro cholerae?

(3 marks)

Answer 8

• Gram negative w/ one flagellum
• Extremely motile
• Oxidase positive

Question 9

What kind of Agar does vibro cholerae grow on?

(2 marks)

Answer 9

• Thiosulfate citrate bile salts - sucrose agar (TCBS)
• Growth in any media with high salt (6% NaCl)

Question 10

What is a reservoir in terms of infection?

Answer 10

Habitat in which agent normally lives, grows and multiplies - can include humans, animals and environment

Question 11

What are the different possible sources of contamination for Vibrocholerae?

(3 marks)

Answer 11

Humans

Water

Microcolony/ Biofilm

(don’t actually know)

Question 12

Why should there technically be no harmful bacteria found on the surface of epithelial cells?

(2 marks)

Answer 12

• Epithelial cell produces lots of antimicrobial protein e.g. IgA which protect the cells
• Should have no bacteria then as blocked by mucus or destroyed by antimicrobial protein

Question 13

What are teh vibrocholerae virulance factors?

Answer 13

T6SS, cholera (etoxin) toxin, TCP (adhesion)

Question 14

What is the mechanism behind the release of cholera toxin?

(4 marks)

Answer 14

1. Bacteria enter epithelium and move towards bottom of villi
2. Once at bottom start to express T6SS and destroy any bacteria present and create desired niche for themselves
3. Start expressing TCP
4. Once nice micro-colony formed, start releasing choleratoxin

Question 15

How does T6SS exert its effects on bacteria?

(3 marks)

Answer 15

• Shoots and injects like harpoon
• Already inside bacteria, bacteria detects another bacteria close to it, ‘harpoon’ will be launched and puncture other protein
• At end of T6SS have protein ERG - has different functions within bacteria

Question 16

How does cholera ensure no othe bacteria are in their desired niche?

(2 marks)

Answer 16

• Uses T6SS to destroy any other bacteria from either different species/ different strain
• Most cells present are amoeba - cholera will use T6SS to kill amoeba and release its bacteria

Question 17

How does cholera toxin avoid macrophage uptake?

Answer 17

VrgG1 cells inhibit phagocytosis protecting vibro cholera from macrophage uptake

Question 18

What does ERG (warhead) do?

(2 marks)

Answer 18

• Target DNA and destroy it
• Create pores in membrane - stopping phaocytosis

Question 19

How does the cholera toxin AB5 induce an effect inside the host?

(2….)

Answer 19

• B subunit will bind to host mebrane and the receptor
• A subunit has catalytic activity and will induce some effect inside host
  
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Question 20

What in particular does the cholera toxin target?

Answer 20

G protein cycle

Question 21

What is the normal mechanism of the G protein cycle?

(6 marks)

Answer 21

• Normally G protein inactive as bound to GDP
• Give activation, GDP replaced by GTP
• Changes conformation of Gsα subunit which deattatches from Gß/γ subunit
• Gsα subunit interacts with adenylyl cyclase which starts the production of cAMP
• cAMP activates PKA
• GTP formed back into GDP and cycle starts again

Question 22

How does the cholera toxin modify the G protein cycle?

(5 marks)

Answer 22

• Modifies arginine and adds adenosine
• Arginine is used to catalyse GTP to GDP
• Causing Gsα to stay in its active form
• Therefore GTP isn’t digested into GDP
• Massive volume of cAMP and massive production of PKA

Question 23

What happens afte there is a major increase in PKA?

(2 marks)

Answer 23

• Phosphorylates CTFR and keeps it open so all Cl is removed from cell and lost in lumen
• This increases movement of H₂O to compensate for loss of Cl causing watery diarrhea

Question 24

What are some prevention methods that can be used to avoid cholera?

Answer 24

Breast feeding for 1st 6 months of age, good personal and food hygeine

Question 25

How can you control the infection of cholera?

(2 marks)

Answer 25

• Rehydration - oral rehydration salts: absorbed in small intestine and replaces water and electrolytes lost in faeces
• Antibitotics - reduce duration of diarrhea episode and reduce stool volume

Question 26

What are the two types of type IV pili?

(4 marks)

Answer 26

• A filamentous tructure found in numerous bacteria

Type IVa:

• widespread, involved in cell motility, DNA transfer, host predation and electron transfer

Type IVb:

• Less prevalent and mainly found in enteropathogenic bacteria involved in host colonisation