GI infections

Question 1

Name the two mechanisms by which bacteria that cause GI infections can be classified into

Answer 1

Infection - bacterial pathogens develop in the gut after the ingestion of contaminated food e.g. salmonella
Intoxication - bacterial pathogens grow in food and produce toxins e.g. bacillus cereus

Question 2

Diarrhoea

Answer 2

o	Abnormal frequency and/or fluid stool
o	Usually indicates small bowel disease
o	Causes fluid and electrolyte loss
o	Severity varies widely from mild self-limiting to severe/fatal
	Virulence of organism
	Degree of compromise of the host

Question 3

Gastroenteritis

Answer 3

o Nausea, vomiting, diarrhoea and abdominal discomfort

Question 4

Dysentery

Answer 4

o Inflammatory disorder of the large bowel
o Blood and pus in faeces
o Pain, fever and abdominal cramps

Question 5

Enterocolitis

Answer 5

o Inflammatory process affecting small and large bowel

Question 6

how is campylobacter infection spread

Answer 6

via contaminated food

Question 7

Describe the campylobacter bacteria

Answer 7

gram-negative bacilli. They are microaerophillic and thermophillic.

Question 8

Give the clinical effects of campylobacter infection

Answer 8

o	Incubation 2-5 days
o	Bloody diarrhoea
o	Cramping abdominal pain
o	Vomiting is not usually a feature
o	Fever
o	Duration 2-10 days

Question 9

Describe pathogenesis of campylobacter infection

Answer 9

o Inflammation, ulceration & bleeding in small and large bowel due to bacterial invasion. Can cause a bacteraemia (elderly and immunocompromised)as well as Guillan barré syndrome

Question 10

How would you treat campylobacter infection

Answer 10

Fluids, clarithromycin in severe/resistant cases. You would give quinolones or an aminoglycoside if the disease was invasive.

Question 11

what species causes the majority of salmonella infection

Answer 11

Salmonella enterica

Question 12

Describe the salmonella bacteria

Answer 12

Gram negative bacilli. Non-lactose fermenters

Question 13

How is Salmonella generally acquired

Answer 13

through ingestion of infected food stuffs (especially pork, poultry and meat). Waterborne infection if less common.
Can have large outbreaks as can multiply in food.

Question 14

Describe pathogenesis of salmonella infection

Answer 14

o Diarrhoea due to invasion of epithelial cells in the distal small intestine, and subsequent inflammation
o Bacteraemia can occur (extremes of age, immunocompromised)
o Distant organs may become seeded to establish metastatic foci of infection e.g. osteomyelitis, septic arthritis, meningitis etc.

Question 15

Clinical features of salmonella infection

Answer 15

o	Incubation 12-72 hours
o	Watery diarrhoea
o	Vomiting is common
o	Fever can occur, and is usually associated with more invasive disease
o	Duration 2-7 days

Question 16

Treatment of Salmonella

Answer 16

o Fluid replacement is sufficient in most cases
o Antibiotics reserved for severe infections and bacteraemia
o Beta-lactams, quinolones or aminoglycosides may be used
o Antibiotics and antimotility agents prolong excretion of salmonellae in the faeces

Question 17

Describe the shigella bacteria

Answer 17

Gram negative bacilli. Non-lactose fermenters. Has four species.

Question 18

How is shigella transmitted?

Answer 18

faecal-oral route is the most common. Humans are only reservoir and large outbreaks can occur. Associated with a low infectious dose.

Question 19

Pathoegenesis of shigella

Answer 19

o Organisms attach to and colonise mucosal epithelium of terminal ileum & colon
o Systemic invasion is not a feature
o S.dysenteriae produces a potent protein exotoxin (Shiga toxin) which not only damages intestinal epithelium, but in some patients targets glomerular endothelium causing renal failure as part of haemolytic-uraemic syndrome (HUS)

Question 20

Four types of shigella

Answer 20

 Shigella sonnei associated with milder infections
 Shigella boydii & S.flexneri associated with more severe disease
 Shigella dysenteriae associated with most severe disease

Question 21

Clinical features of shigella infection

Answer 21

o	Dysentery
o	Incubation 1-3 days
o	Duration 2-7 days
o	Initially watery diarrhoea followed by bloody diarrhoea
o	Marked, cramping abdominal pain
o	Vomiting is uncommon
o	Fever is usually present

Question 22

Treating shigella

Answer 22

o Usually self-limiting
o Fluid replacement is usually sufficient
o Some cases of S.dysenteriae infection will require treatment of renal failure
o Specific control points
o Only found in humans, so good standards of sanitation and personal hygiene are key measures

Question 23

Describe the Cholera bacteria

Answer 23

gram negative bacilli, sucrose-fermenter.

Classified on the basis of their O antigens.

Question 24

How does cholera spread?

Answer 24

Spreads via contaminated food or water. Can cause pandemics. Is endemic in parts of SE Asia, S America
Person to person transmission is uncommon

Question 25

Pathogenesis of cholera

Answer 25

o Flagellae and mucinase facilitate penetration of intestinal mucous
o Attachment to mucosa by specific receptors
o Diarrhoea due to production of a potent protein exotoxin

Question 26

Clinical features of cholera

Answer 26

o Severe, profuse, non-bloody, watery diarrhoea (rice water stool)
o Profound fluid loss & dehydration precipitates hypokalaemia, metabolic acidosis, hypovolaemic shock and cardiac failure
o Untreated mortality 30-40%

Question 27

treatment of cholera

Answer 27

o Prompt oral or intravenous rehydration is lifesaving (mortality reduced to <1%)
o Tetracycline antibiotics may shorten duration of shedding

Question 28

Describes the pathogenesis of enteropathogenic E.coli

Answer 28

Initial adherence via pili, followed by formation of characteristic “attatching & effacing” lesion mediated by intimin protein and Tir (translocated intimin receptor) with disruption of intestinal microvilli

Question 29

What is a major bacterial cause of diarrhoea in infants & children in developing world and travellers diarrhoea?

Answer 29

ETEC

Question 30

Summaries pathogenesis of ETEC

Answer 30

Diarrhoea due to action of 1 or 2 plasmid-encoded toxins
 Heat-labile (LT). Structural and functional analogue of cholera toxin
 Heat-stable (ST). Produced in addition to or instead of LT. Similar mode of action

Question 31

Describe the pathogenesis of EHEC

Answer 31

o Attaching and effacing lesion (similar to EPEC)
o Production of Shiga-like toxins. Structural and functional analogue of Shigella dysenteriae toxin (sometimes strains called STEC [shiga-toxin producing EC] or VTEC [verotoxin-producing EC] because toxins are toxic for cultured vero cells

Question 32

Clinical features of EHEC

Answer 32

o	Incubation 1-7 days
o	Duration 5-10 days
o	Bloody diarrhoea with abdominal pain and vomiting
o	No associated fever
o	Haemolytic uraemic syndrome (5-10% of cases)
	Microangiopathic haemolytic anaemia
	Thrombocytopaenia
	Acute renal failure

Question 33

Describe pathogenesis of S.aureus in GI infection

Answer 33

50% of S.aureus produce enterotoxins (types A-E)
Heat stable and acid-resistant protein toxins
Food is contaminated by human carriers
Especially cooked meats, cakes and pastries
Bacteria multiply at room temperature and produce toxins

Question 34

Describe the two types of disease you can develop from B.cereus

Answer 34

Emetic - commonly results from the re-cooking of rice that has already been boiled. The spores survive the initial boiling and then have time to germinate, multiple and re-sporulate. As they resporulate they produce enterotoxin which survives any subsequent frying.
Diarrhoeal disease - Spores survive cooking and then germinate in the food. They are then ingested and produce a heat-labile toxin in the gut which has a similar action to cholera toxin

Question 35

Describe the bacillus cereus bacteria

Answer 35

aerobic, spore-forming gram-positive bacilli.

Question 36

Describe the clinical effects of the two types of B.cereus

Answer 36

Emetic - profuse vomiting with abdominal cramps. Incubation: 30 minutes -6 hours. Duration: 12 -24 hours.
Diarrhoeal - watery diarrhoea with crampy abdominal pain. No vomiting.
 Incubation 8 -12 hours
 Duration 12 -24 hours

Question 37

Describe the C.diff bacteria

Answer 37

anaerobic, gram-positive and spore forming bacilli.

Question 38

Treatment of C.diff

Answer 38

If no severity markers - metronidazole

If 1 or more severity markers - oral vancomycin.

Question 39

How would you treat a H.pylori infection

Answer 39

triple therapy - PPI, clarithromycin and metronidazole.