GI Infections

Question 1

Explain how the microbiome changes across the length of the GI tract.

Answer 1

Stomach is there to disinfect food. Some bacteria, such as H. pylori, can thrive in this ‘microaerophilic’ environment where there is some O2 but less than in the air. The small bowel is relatively sterile but there is an enormous amount of bacterial matter in the colon. 20% of the mass of faeces is bacteria.

Question 2

What benefits do we get from the gut microbiome?

Answer 2

• Commensals out-compete harmful bacteria for nutrients.
• Microbiome produces antimicrobial substances.
• Conditions a newbowns immune system toward a Th1 response.
• Produce nutrients such as Vitamin K.

Question 3

How does vaginal delivery effect the microbiome?

Answer 3

Baby picks up vaginal commensals. We know vaginally delivered babies have a better gut microbiota than those delivered by C-section.

Question 4

What role does the microbiome play in colonocyte function?

Answer 4

Produces short chain fatty acids that act as an energy source for colonocytes (e.g. butyrate). Other SCFA’s such as propionate regulate satiety.

Question 5

What microbiotal changes are seen in obesity and IBD?

Answer 5

There is less diversity.

Question 6

What effect does the Microbiome have on the body’s response to insulin or chemotherapy.

Answer 6

The microbiome seems to affect the response of the body to food, in terms of insulin production and the response to chemotherapy.

Question 7

What is the difference between probiotics and prebiotics?

Answer 7

Probiotics = live bacterial cultures ingested. 
Prebiotics = a nutrient medium for the microbiome.

Question 8

What effect could a diet high in sweetners, meat contaminated with antibiotics and gluten free foods in those who don’t need them cause?

Answer 8

Potentially detrimental decrease in the diversity of the gut flora.

Question 9

Give some methods for administering a faecal microbiota transplant?

Answer 9

Either upper GI endoscopy or colonoscopy. NG tubes or tubes into duodenum are less palatable to patients.

Question 10

Give two potential indications for faecal microbiota transplant?

Answer 10

• Crohn’s disease.
• C. difficile infections. Here, it is highly successful at achieving diarrhoea remission - 3x more-so than Vancomycin treatment.

Question 11

Give an example of some of the criteria to be a faecal donor?

Answer 11

Age 10-25. Good health. No use of laxatives, diet pills or Abx in the past three months. No GI disease or infectious disease.

Question 12

Give some symptoms of Salmonella infection.

Answer 12

Nausea, Vomiting, Non-Bloody Diarrhoea, Fever, Abdominal cramps.

Question 13

Describe the time course of a Salmonella infection.

Answer 13

Symptoms develop c.48 hours after eating contaminated food and continue for 2-3 days after which the body clears the infection.

Question 14

Describe the pathology of a salmonella infection within the gut?

Answer 14

• Invades enterocytes.

- Enters macrophages which transport it to the RES. Here it causes lymphoid hyperplasia and re-enters gut from liver.

Question 15

How is the course of Campylobacter different to Salmonella?

Answer 15

Both are faecal oral transmission. Compared to a 48 hour incubation period Campylobacter has an incubation period of 1-7 days and the diarrhoea (which may be bloody) can last from days to weeks.

Question 16

How would you treat an infection with Campylobacter?

Answer 16

• Abx if stool is bloody.

- Oral rehydration fluids and bland diet.

Question 17

How does campylobacter do its damage?

Answer 17

Similarly to cholera, it produces a cytotoxin.

Question 18

Describe Shigella.

Answer 18

A gram negative bacterium causing Shigellosis in small children. Needs a small dose to infect. It invades colonocytes, killing them and then invading neighbouring cells, forming abscesses in tissues. It causes bloody diarrhoea (with mucus) but usually resolves WITHIN A WEEK.

Question 19

What group of people typically get enterotoxigenic E. coli?

What does it do?

Answer 19

Travellers. Picked up from contaminated water. It invades enterocytes, producing enterotoxins causing hypersecretion of chloride ions. Water leaves cells into the gut lumen giving watery diarrhoea.

Question 20

Give a rough order of the time course of the infections caused by gram negative organisms (shortest to longest).

Answer 20

Enterotoxigenic E. Coli –> Salmonella –> Shigella –> E. Coli.

Question 21

Which of the gram negative rods can lead to Haemolytic Uraemia syndrome?

Answer 21

• Shigella

- Campylobacter.

Question 22

How would we classify the bacterium C. difficile?

Answer 22

It is a gram positive, spore forming bacillus.

Question 23

What is the characteristic patient presentation with a C. diff infection?

Answer 23

Patient has been in hospital recently, treated with Abx. People have a spectrum of symptoms from nothing to severe diarrhoea +/- abdominal cramps. Diarrhoea is very rarely bloody though.

Question 24

Name two major complications of C. difficile?

Answer 24

• Pseudomembranous colitis (many inflamatory cells and exudate form a ‘false membrane’ on top of the gut mucosa). Elevated yellow plaques that steadily join.
• Toxic megacolon.

Question 25

What is the pathophysiology of C. difficile infection?

Answer 25

Produces two toxins. Toxin A is an enterotoxin (leading to excessive secretion while toxin B is a cytotoxin.

Question 26

Give a common cause of viral gastroenteritis in under 5s?

Answer 26

Rotavirus (now vaccinated against). You get a mixed diarrhoea with Cl- secretion being accompanied with increased osmotic loading as SGLT1 is disrupted as are brush border enzymes.

Question 27

Does rotavirus commonly affect adults?

Answer 27

No, people gain their immunity in childhood and carry this through into adulthood.

Question 28

Give a major cause of viral gastroenteritis that affects all age groups.

Answer 28

Norovirus. You can’t develop any meaningful immunity as there are so many strains. Resistant to most disinfectants. Incubation is 1-2 days and symptoms last 1-3 days. Quite similar to Salmonella in time course.

Question 29

What is the mechanism of diarrhoea and vomiting in norovirus infection?

Answer 29

Norovirus increases vomiting risk by delaying gastric emptying. Diarrhoea is caused by induced brush border enzyme disruption and Cl- ion secretion.

Question 30

How long does the diarrhoea last for in Rotavirus?

Answer 30

1 week; similar to Shigellosis which affects a similar age group of children.

Question 31

Talk about Cryptosporidium.

Answer 31

This is a protozoa which can cause GI infections. It has a faecal oral spread, including via water contaminated by animal faeces. People at risk are involved in changing nappies, backpackers, people who swim in open water and people handling infected cows.

Question 32

Talk about the life cycle of a cryptosporidium parasite?

Answer 32

People ingest oocysts which reproduce inside small intestine epithelia causing brush border dysfunction and chloride secretion before being expelled into the intestine, also as an oocyst.

Question 33

Which group of people may benefit from antiparasitic treatment in the case of a Cryptosporidium infection?

Answer 33

People with AIDS or other immunocompromise.

Question 34

What infection is the commonest cause of persistent diarrhoea?

Answer 34

Giardia, a protozoa. Again, it has a faecal oral spread and can be spread by poorly prepared food, water and faeces. Diarrhoea can last for up to 6 weeks.

Question 35

What is the incubation period for a giardial infection?

Answer 35

10+ days.

Question 36

What is the life cycle of a giardial parasite?

Answer 36

Cyst is ingested. It multiplies in the small intestine causing damage to brush border and villi. It then passes into the colon where it enters the cyst stage.

Question 37

What treatment is needed in Giardial infection?

Answer 37

Antibiotics and oral rehydration.

Question 38

After an infection with giardia, what GI problem may people experience?

Answer 38

Lactase deficiency is common so people may experience lactose intolerance. Go back to consuming dairy slowly.

Question 39

Where in the world may you see infections with Entamoeba histiolytica? What is the spectrum of disease?

Answer 39

Developing countries. Disease asymptomatic in 80% of cases, if it is symptomatic it may lead to diarrhoea or even liver abscesses in rare cases.

Question 40

What is the pathophysiology in Entamoeba infection?

Answer 40

Cysts travel into the colon where trophozoites invade mucosa causing bloody diarrhoea. If the infection spreads to the liver, abcesses can form.

Question 41

What are two potentially serious sequelae to an infection with Entamoeba histiolytica?

Answer 41

• Liver abscess

- Severe colitis/toxic megacolon.

Question 42

How can we define diarrhoea and break it down into mild/moderate and severe?

Answer 42

Diarrhoea = passing more than 3 stools in 24 hours. 
3-6 = mild/moderate.
6+ = severe; this may be an indication for Abx and IV fluids.