Bacterial and Viral Infections of the GI Tract

Question 1

What are the normal barriers to infection in the GI tract?

Answer 1

• Stomach acidity,
• Normal flora,
• peristalsis,
• antimicrobial compounds

Question 2

What is the difference between intoxication and infection.

Answer 2

Intoxication - Ingestion of food containing biologically active toxins which cause disease.

Infection - Ingestion of live microbes which can go on to multiply on food pre consumption and use food as a vector

Question 3

Describe methods of diagnosis for GI infections

Answer 3

• History and examination but this is very difficult, some useful clues ae dysentery, vomiting, abdo pain, travel, food and speed of onset.
• Microbiology

Question 4

Describe the general treatment for GI Tract infections

Answer 4

• Most resolve spontaneously and only require fluid replacement but for severe/prolonged cases then antibiotics can be used.

Question 5

Explain why the use of antibiotics can worsen a disease?

Answer 5

By prolonging duration, promoting toxin release and increasing antibiotic resistance

Question 6

Explain oral rehydration therapy and why it is clinically useful

Answer 6

Use of oral hydration salts, this speeds up hydration because as sodium and glucose are absorbed through the gut wall, water follows by osmosis

Question 7

Name the three main viral infections

Answer 7

Norovirus, Rotavius and adenovirus

Question 8

Explain the pathogenesis and clinical presentation of norovirus (single stranded RNA virus)

Answer 8

It requires a very small infectious dose 10-100 virions. It causes projectile vomiting, diarrhoea, abdo cramps, headaches, muscle aches

Question 9

Explain the pathogenesis and clinical presentation of the Rotavirus (double stranded RNA virus)

Answer 9

• Mainly affects young children (but gives life long immunity), elderly and immunocompromised however live attenuated oral vaccine produced.. Infectious dose very small.
• Causes watery diarrhoea, vomiting, abdo cramps, fever.

Question 10

Explain the pathogenesis and clinical presentation of the Adenovirus (double stranded DNA virus)

Answer 10

• Effects the young, old and immunocompromised. Small infectious dose.
• Mild prolonged diarrhoea

Question 11

Name the possible gram negative bacteria

Answer 11

• Campylobacter,
• Vibrio Cholerae,
• Salmonella,
• Shigella,
• Escherichia Coli,
• Yersinia enterocolitica

Question 12

Describe features of Campylobacter

Answer 12

• Gram neg curved bacilli with flagella which is transmitted via animals and contaminated food.
• Pathogenesis - Invasion of the bowel leads to inflammation and ulceration,
• Symptoms include bloody diarrhoea, abdo pain and fever

Question 13

Describe features of vibrio cholera?

Answer 13

• Gram neg bacilli,
• Pathogenesis - Polar flagella with mucinase which facilitate penetration of intestinal mucous, . Disease is caused by exotoxin.
  Symptoms - severe, profuse, watery diarrhoea. Profound fluid and electrolyte loss and hypovolaemic shock and cardiac failure.

Question 14

How is vibrio cholera transmitted?

Answer 14

Contaminated food or water. Therefore clean water supply and proper sanitation is key.

Question 15

Explain how the cholera toxin works?

Answer 15

• Subunit B binds to the receptor on the surface of cells. Subunit A refolds and becomes active and promotes the activity of adenylate cyclase which activates cAMP. cAMP pushes chloride ions out of the cell and since they are negative, positive Na follows and then so does water due to osmosis

Question 16

Describe features of salmonella

Answer 16

• Gram neg bacilli.
• Pathogenesis - Invasion and inflammation of the bowel; Absorbed at terminal ileum, multiples in peyer’s patches. Inflammatory response mediates release of prostaglandins which stimulates cyclic AMP.
• Symptoms = watery diarrhoea, vomiting and fever

Question 17

What are the clinical features of enteric fevers (Typhoid, paratyphoid)

Answer 17

• Malaise, headache, cough, rose spot rash, fever, bradycardia (rare as fever normally causes tachycardia), severe lethargy, constipation, hepatosplenomegaly and intestinal haemorrhage

Question 18

Describe features of shigella

Answer 18

• Gram neg bacilli,
• Pathogenesis = production of shiga toxin (exotoxin) which damages intestinal epithelium. The toxin can cause haemolytic uremic syndrome.
• Symptoms = Watery followed by bloody diarrhoea, cramping abdo pain and fever

Question 19

Describe features of enterotoxigenic Eshcerichia coli

Answer 19

• Pathogenesis = Diarrhoea due to toxins. Heat-labile (LT); structural and functional analogue of cholera toxin. Heat-stable (ST); produced in addition to or instead of LT (Causes formation of cGMP).
• Symptoms = Watery diarrhoea, abdo pain and vomiting.

Question 20

Describe features of enterohaemorrhagic E.coli

Answer 20

• Pathogenesis = Production of shiga-like toxins which target the glomerular endothelium causing haemolytic uremic syndrome.
• Symptoms = bloody diarrhoea, abdo pain and vomiting. AVOID antibiotics as they promote toxin release.

Question 21

What is the most common cause of acute renal failure in children in the UK?

Answer 21

E.coli 0157

Question 22

What is haemolytic uremic syndrome?

Answer 22

Haemolytic uremic syndrome (HUS) is a group of blood disorders characterized by low red blood cells, acute kidney failure, and low platelets

Question 23

Describe features of Yersinia enterocolitica

Answer 23

• Pathogenesis = invasion of terminal ileum with inflammation of mesenteric lymph nodes.
• Symptoms = Bloody diarrhoea, abdominal pain and fever. Mesenteric adenitis may mimic acute appendicitis. Often only supportive therapy is required

Question 24

Name some gram positive bacteria

Answer 24

• Staphylococcus aureus,
• Clostridium botulinum,
• Clostridium difficile,
• Listeria monocytogenes

Question 25

Describe features of staphylococcus aureus

Answer 25

• Transmitted via food contaminated by carriers.
• Pathogenesis = heat stable and acid-resistant protein toxins results in emetic disease.
• Symptoms = profuse vomiting and abdominal cramps but NO diarrhoea or fever

Question 26

Describe features of clostridium botulinum

Answer 26

Pathogenesis - Produces powerful heat-labile protein neurotoxin. Absorbed toxins spread via bloodstream and enter peripheral nerves where they cause neuromuscular blockade.

Symptoms - Neuromuscular blockade results in flaccid paralysis and progressive muscle weakness, can lead to resp failure. High mortaility if untreated. Can use antitoxins

Question 27

Describe features of clostridium difficile

Answer 27

Pathogenesis - Disruption of normal protective gut flora due to antibiotics, chemo or antacids. Release of toxins A and B.
- Symptoms = mild to severe diarrhoea, psudomembranous colitis, toxic colon dilation or perforation.

Question 28

What is the treatment for C.difficile?

Answer 28

• Stop precipitating antibiotics,
• Oral metronidazole or vancomycin,
• Faecal transplant

Question 29

Describe features of listeria monocytogenes

Answer 29

• Transmitted via contaminated foods.
• Pathogenesis = invasive infection.
• Symptoms = Initial flu-like illness with/without diarrhoea, can cause severe systemic infection. IV antibiotics are needed

Question 30

Describe features of helicobacter pylori

Answer 30

• Gram neg,
• Pathogenesis = Cytotoxin production and a range of factors to promote adhesion and colonisation. Produces urease to generate ammonia from urea and elevates pH
• Asymptomatic unless ulceration develops.

Question 31

What is the diagnosis and treatment of helicobacter pylori

Answer 31

Diagnostics - Faecal antigen, serology treatment, C-urea breath test and culture from biopsy.
Treatment - One week therapy with proton pump inhibitor (PPI) and two antibiotics