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ACEM Primary Written > Infectious diseases: Pathology - Gastrointestinal infection > Flashcards

Infectious diseases: Pathology - Gastrointestinal infection Flashcards

1
Q

What type of bacteria is Vibrio cholerae?

A

Gram-negative comma-shaped

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2
Q

What are the three virulence factors of Vibrio cholerae?

A
  1. Flagella: for motility and adherence
  2. Cholera toxin
  3. Haemagglutinin: for detachment and shedding in stool
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3
Q

Describe the structure and function of the cholera toxin

A

Composed for five B subunits and one A subunit
B subunit binds epithelial cell membrane for endocytosis of the toxin
Once inside cytosol, A subunit is transported and refolded
Refolded A subunit activates Gs -> stimulates adenylyl cyclase -> increased cAMP -> CFTR Cl- channel opening -> Cl- release
Results in release of HCO3-, Na+ and H2O, with impaired reabsorption of Cl- and Na+ -> produces massive secretory diarrhoea (up to 1L/hr)

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4
Q

What is the most common bacterial enteric pathogen in the developed world?

A

Campylobacter

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5
Q

What is the usual method of transmission of Campylobacter?

A

Often associated with uncooked chicken (may also be associated with unpasteurised milk or contaminated water)

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6
Q

What are the three virulence factors of Campylobacter?

A
  1. Flagella: for motility and adherence
  2. Cytotoxins: including some which produce a Cholera-like toxin
  3. Invasion: small minority of strains are invasive and cause dysentery (15%)
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7
Q

Three complications of Campylobacter infection

A
  1. Reactive arthritis
  2. Erythema nodosum
  3. Guillain-Barre syndrome
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8
Q

What is the incubation period for Campylobacter? How long do infected individuals shed for?

A

Incubation period up to 8 days
Shedding occurs for up to 1 month post clinical resolution

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9
Q

What type of bacteria is Campylobacter jejuni?

A

Gram-negative comma-shaped

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10
Q

What type of bacteria is Shigella spp?

A

Gram negative bacillus
Unencapsulated and non-motile
Facultative anaerobe
Related to E. coli

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11
Q

What infectious picture is caused by Shigella spp?

A

Dysentery which may wax and wane for ~1 month
May mimic first presentation ulcerative colitis

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12
Q

Two complications of Shigellosis

A
  1. Reiter syndrome: triad of sterile arthritis, urethritis, conjunctivitis
  2. HUS
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13
Q

What type of bacteria is Salmonella?

A

Gram negative bacillus

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14
Q

What is the usual mode of transmission of salmonella?

A

In raw or undercooked meat, poultry, eggs and milk

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15
Q

Which organism is the usual cause of nontyphoid Salmonella?

A

Salmonella enteritidis

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16
Q

What organism causes typhoid fever?

A

Salmonella typhi and paratyphi

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17
Q

How is typhoid transmitted?

A

Person-to-person or faecal-oral

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18
Q

Describe the pathogenesis of typhoid fever

A

Taken up by M cells in small intestine, then engulfed by mononuclear cells in underlying lymphoid tissue
Then disseminated via lymphatic and blood vessels -> reactive hyperplasia of phagocytes and lymphoid tissues throughout body

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19
Q

Describe the clinical features of typhoid fever

A

Acute syndrome of anorexia, abdominal pain, bloating, nausea and vomiting, and dysentery
Followed by short asymptomatic phase that then gives way to bacteraemia, fever and flu-like symptoms
Other features include Rose spots on chest and abdomen, ileal ulcers (+/- perforation), and splenomegaly

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20
Q

Eight complications of typhoid fever

A
  1. Encephalitis
  2. Meningitis
  3. Seizures
  4. Endocarditis
  5. Myocarditis
  6. Pneumonia
  7. Cholecystitis
  8. Osteomyelitis (especially in setting of sickle cell)
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21
Q

Which complication of typhoid fever is more common in patients with sickle cell disease?

A

Osteomyelitis

22
Q

How does typhoid progress to chronic carrier state?

A

Through asymptomatic colonisation of gallbladder

23
Q

What type of bacteria is Yersinia?

A

Gram negative bacillus
Facultative intracellular bacteria

24
Q

How is Yersinia transmitted?

A

From contaminated pork, raw milk, and contaminated water

25
Q

What enhances the virulence of Yersinia?

A

Iron (those with haemolytic anaemia or haemochromatosis at risk of severe illness)

26
Q

Three extra-intestinal symptoms of Yersinia infection

A
  1. Pharyngitis
  2. Arthralgia
  3. Erythema nodosum
27
Q

Five complications of Yersinia infection

A
  1. Sterile arthritis
  2. Reiter syndrome
  3. Myocarditis
  4. Glomerulonephritis
  5. Thyroiditis
28
Q

What type of bacteria is E. coli?

A

Gram negative bacillus

29
Q

Four subsets of E. coli

A
  1. Enterotoxigenic (ETEC)
  2. Enterohaemorrhagic (EHEC)
  3. Enteroinvasive (EIEC)
  4. Enteroaggregative (EAEC)
30
Q

What is the principal cause of traveller’s diarrhoea?

A

ETEC

31
Q

What two toxins are produced by ETEC?

A
  1. Heat-labile toxin (LT): similar to cholera toxin -> increased cAMP -> increased Cl- secretion
  2. Heat-stable toxin (ST): activation of guanylyl cyclase -> increased cGMP -> increased Cl- secretion
32
Q

What are the subtypes of EHEC?

A

O157:H7
Non O157:H7

33
Q

What toxins are produced by EHEC?

A

Shiga-like toxins

34
Q

What kind of clinical syndrome is caused by EHEC?

A

Dysentery

35
Q

How is O157:H7 E. coli spread and what is a complication?

A

Associated with contaminated ground beef
Can cause HUS

36
Q

How is EIEC transmitted?

A

Via food, water, and person-to-person contact

37
Q

What toxins do EIEC produce?

A

Do not produce toxins but invade epithelial cells

38
Q

Describe the pathogenesis of EAEC

A

Attach to enterocytes via adherence fimbriae, aided by dispersin (bacterial surface protein that neutralises negative surface charge of LPS)
Produce enterotoxins related to Shigella and ST enterotoxins (but damage minimal)

39
Q

Which subtype of E. coli produces diarrhoeal illness which is prolonged in those with AIDS?

A

EAEC

40
Q

What is pseudomembranous colitis?

A

Antibiotic-associated colitis, commonly caused by Clostridium difficile
May also be immunosuppression-related

41
Q

Which antibiotics most often cause pseudomembranous colitis?

A

3rd gen cephalosporins

42
Q

Three risk factors for pseudomembranous colitis

A
  1. Advancing age
  2. Hospitalisation (up to 30% of hospitalised adults are colonised)
  3. Antibiotic treatment
43
Q

Describe the pathogenesis of pseudomembranous colitis

A

Disruption of normal flora by antibiotics results in C. difficile overgrowth
Toxins are released and cause ribosylation of small GTPases, resulting in:
- Disruption of epithelial cytoskeleton
- Tight junction barrier loss
- Cytokine release
- Apoptosis

44
Q

Describe the two morphological of pseudomembranous colitis

A
  1. Formation of pseudomembranes (adherent layer of inflammatory cells and debris at sites of colonic mucosal injury: not specific to pseudomembranous colitis, can be caused by ischaemia/necrosis)
  2. Superficially damaged crypts distended by mucopurulent exudate -> eruption reminiscent of volcano
45
Q

What are the three most common causes of viral gastroenteritis? What type of virus is each?

A
  1. Norovirus: ssRNA
  2. Rotavirus: dsRNA
  3. Adenovirus: dsDNA
46
Q

What is the most common cause of childhood diarrhoea?

A

Rotavirus

47
Q

Describe the pathophysiology of virus gastroenteritis

A

Diarrhoea results from destruction of superficial epithelial cells -> malabsorption of Na+ and H2O -> osmotic diarrhoea

48
Q

Describe the pathogenesis of entamoeba histolytica

A

Amoebe attaches to colonic epithelium, induces apoptosis, invade into crypts and lamina propria
Creates flask-shaped ulcer
May penetrate splanchnic vessels and embolise to liver (can form abscesses)

49
Q

What is the most prevalent pathogenic parasitic infection in humans?

A

Giardia lambia

50
Q

Describe the pathogenesis of Giardia

A

Decreased expression of brush border enzymes
Microvillous damage
Apoptosis of small intestinal epithelial cells
Evades immune clearance by continuous modification of major surface antigen

51
Q

What kind of diarrhoeal syndrome is caused by Giardia?

A

Malabsorptive diarrhoea

52
Q

How does cryptosporidium cause diarrhoea?

A

By means of sodium malabsorption, chloride secretion, and increased permeability of tight junctions

ACEM Primary Written (160 decks)

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