Gastrointestinal infections

Question 1

What are the major presentations of gastro-intestinal infections? Please, describe the clinical symptoms for one of them and give 2 examples for associated pathogens.

Answer 1

Usually GIT infections are present with gastrointerstinal symptoms like diarrhoea and abdominal d
pain.
they may spread to other parts of the body (extraintestinal infections)

Diarrhoea is the passing loose fluid stools more than 3times a day or more than the individuals regular frequency of passing stool.
pathogens- Vibrio cholera, Rotavirus and eschreichia coli.

Question 2

What is a zoonotic disease?

Answer 2

an infection or disease which under natural conditions can be transmitted between humans and animals.
eg. Rabies, anthrax and bird flu

Question 3

Name 3 intestinal signals, what they are an indicator for and a pathogen that senses them.

Answer 3

1. Metabolic signals- Bile acid (Vibrio cholera), Fructose (E. coli)
2. Physico-chemical signals- Osmolality and oxygen tension (salmonella)
3. Mechanocal signals- attachment (E. coli) and Viscosity (Vibrio)
4. quorum sensing- Cell density (staph. aureus)

Question 4

What is a type-3-secretion system? Please, describe the mechanism of action and name 2 pathogenic species, that employ them during infection.

Answer 4

it is a needle like structure (like a needle and syringe) possesed by some gram negative bacteria which inject bacterial effector proteins.
Campylobacter, salmonella, Escherichia, Pseudomanas.

Question 5

What is the full taxonomic name of Salmonella Typhimurium?

Answer 5

Salmonella enterica ssp. enterica (I) serovar Typhimurium

Question 6

Name 2 Salmonella-Serotypes, that cause extra-intestinal infections and that are restricted to humans.

Answer 6

Salmonella Typhi
Salmonella paptyphi A and C
Salmonella Dublin

Question 7

Explain one mechanism how extra-intestinal Salmonella serotypes evade immune recognition. Name the corresponding
serotype.

Answer 7

Salmonella serotypes have diveloped different meachnisms to prevent igM binding.

S. parayphi has very long LPS with O2 antigen which is not able to be bound by IgM.
S. typhi with capsule having V1 antigen which prevents binding LPS to IgM.

Question 8

Please describe the composition and mechanism of action of the cholera toxin of Vibrio cholerae.

Answer 8

Cholera Toxin A- mono ADP- ribosyltransferase
Chlolera Tpxin B- 5 subunits which have receptor binding capacity.

MoA- Firt the B subunit binds to GM1 gangliosides on intestinal epithelia.
Once bound the toxin is endocytosed the A1 subunit separates itself to catalyse the ribosylation of ADP on the G alpha subunit. This ribosylation results in permanent activation of G alpha leading to increased adenylate cyclase activity

irrreversible increase in adenylate cyclase activity causes the opening of chloride channels which induces loss of water and elctrolytes from the body in the form of diarrhoea.

Question 9

Why can O-antigens not be used for serotyping of C. difficile isolates?

Answer 9

a

Question 10

How do antibiotics increase the risk of contracting an infection with C. difficile? Choose one example and explain.

Answer 10

Use of antibiotics disrupt the host response to bacteria which leads to a shift in metabolic environment.
This allows host be susceptible agian due to loss of colonization resistance.