MI: GI infections Pt.1

Question 1

List some reportable GI infections

Answer 1

• Camplybacter
• Salmonella
• Shigella
• Escherichia coli O157
• Listeria

Question 2

What are the main characteristics of secretory diarrhoea? What are some causes?

Answer 2

• No fever/low grade fever
• No inflammatory cells in stool
• Causes: Vibrio Cholera, ETEC

Question 3

What are the main characteristics of inflammatory diarrhoea? What are some causes?

Answer 3

• Fever
• Inflammatory cells present in stool (neutrophils)
• Causes: Campylobacter jejuni, Shigella, non-typhiodal Salmonella, EIEC

Also known as exudative diarrhoea

Question 4

List some examples of severe GI infections that produce a fever with little stool changes.

Answer 4

Also known as enteric fever

• Salmonella typhi
• Enteropathogenic Yersinia
• Brucella

White blood cells are present in stool (mononuclear cells)

Question 5

Describe the mechanism by which Vibrio cholerae causes secretory diarrhoea.

Answer 5

• The cholera toxin has subunits A and B which stimulate adenylate cyclase.
• This leads to the production of cAMP which opens chloride channels on the membranes of enterocytes.
• Chloride efflux into the lumen is accompanied by water and electrolyte loss.

Question 6

What are superantigens?

Answer 6

• Toxins that bind to TCR and MHC outside the peptide binding region
• This leads to non-specific activation and large-scale polyclonal expansion of T cells with massive cytokine production
• Results in systemic toxicity and suppression of adaptive immune response

Question 7

How does the host immune response determine in inflammatory respone to enteropathic bacteria?

Answer 7

Question 8

What type of organism is Staphylococcus aureus?

Answer 8

• Gram-positive coccus
• Catalase and coagulase positive
• Appears in clusters

Question 9

What type of toxin is produced by Staphylococcus aureus?

Answer 9

Enterotoxin - this is an exotoxin that can act as a superantigen in the GI tract triggering the release of IL1 and IL2

Question 10

How is Staphylococcus aureus spread and what kind of GI symptoms can it cause?

Answer 10

• Spread by skin lesions on food handlers
• Causes prominent nausea and vomiting (occasionally watery diarrhoea)
• Self-limiting (resolution within 24 hours) so does not require treatment

Question 11

What type of organisms is Bacillus cereus?
Associated food?

Answer 11

Gram-positive rods that are spore-forming

Spores germinate in reheated rice

Question 12

What type of toxins does B. cereus produce?

Answer 12

• Heat-stable emetic toxin
• Heat-labile diarrhoeal toxin

Question 13

What type of GI symptoms does B. cereus cause?

Answer 13

Diarrhoeal type - watery, non-bloody diarrhoea; abdominal cramping

Emetic type - nausea and vomiting (sometime diarrhoea as well)

NOTE: it can cause bacteraemia and cerebral abscesses in vulnerable populations

Question 14

Name three types of Clostridium infection

Answer 14

• Clostridium botulinum
• Clostridium perfringens
• Clostridium difficile

Question 15

What kind of infection does Clostridium botulinum cause?

Associated foods?

Treatment?

Answer 15

Causes botulism - ptosis, double vision, dysphagia, progessive muscle weakness and paralysis

• From canned food
• Causes disease due to preformed toxin which blocks acetylcholine release at peripheral nerve synapses resulting in paralysis
• Treated with antitoxin

Question 16

What kind of infection does Clostridium perfringens cause?

Answer 16

Causes food poisoning - watery diarrhoea, cramps, but NO vomiting that lasts 24 hours

• From undercooking and poor storage of meat
• Part of normal colonic flora, but NOT small bowel
• Creates enterotoxic superantigen affects small bowel

Question 17

What kind of infection does C. difficile cause?

Answer 17

Pseudomembranous colitis

• Hospital-acquired infection related to antibiotic use

Question 18

Which antibiotics are most commonly implicated in C. difficile colitis?

Answer 18

• Cephalosporins
• Clindamycin
• Ciprofloxacin

Question 19

How is C. difficile colitis treated?

Answer 19

• Metronidazole, vancomycin
• Stop the offending antibiotic

Question 20

What type of organism is Listeria monocytogenes?

Answer 20

• Gram positive, rod-shaped, facultative anaerobe
• Beta-haemolytic, aesculin-positive with tumbling motility

Question 21

What is the source of Listeria?

Answer 21

Grows are 4 degrees so refrigerated foods (cold enhancement)

• Unpasteurised dairy
• Vegetables

Question 22

What GI symptoms does Listeria tend to cause? Which patients groups are particularly susceptible?

Answer 22

• Fever, watery diarrhoea, cramps, headache and NO vomiting
• Neonates, immunocompromised

Question 23

How is Listeria infection treated?

Answer 23

Ampicillin

Question 24

What type of organisms are Enterobacteriaceae and name some examples?

Answer 24

• Facultative anaerobes
• Lactose fermenters
• Oxidase-negative
• Escherichia coli, Salmonella, Shigella, Klebsiella

Question 25

Name and describe the different types of E. coli infection.

Answer 25

• ETEC - toxigenic, main cause of travellers’ diarrhoea
• EPEC - pathogenic, infantile diarrhoea
• EIEC - invasive, dysentry
• EHEC - haemorrhagic, caused by E. coli 0157:H7

Avoid antibiotic treatment

Question 26

Where does E. coli act?

Answer 26

Jejunum, ileum but NOT colon

Question 27

Which toxin causes haemolytic uraemic syndrome?

Answer 27

EHEC shiga-like verocytotoxin