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MD3002 Pathology > Bacterial and Viral Infections of the GI tract > Flashcards

Bacterial and Viral Infections of the GI tract Flashcards

1
Q

How can GI pathogens damage the body?

A
  • Local inflammation
  • Ulceration / perforation of mucosal epithelium
  • Disruption of normal gut microbiota
  • Pharmacological action of bacterial toxins
  • Invasion into blood or lymphatics
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2
Q

What can happen as a result of a ruptured / perforated ulcer?

A
  • May result in leaking of food and gastric juices to the peritoneal or abdominal cavities
  • Treatment requires surgery
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3
Q

What can happen to the villi as a resultof E. coli invasion?

A

Vilous atrophy

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4
Q

What are the stools like of someone affected by EPEC and cholera?

A

Watery

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5
Q

What bacterial infections can cause bloody stools?

A

Campylobacter and Shigella

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6
Q

Give some examples of bacterial diarrhoeal pathogens?

A
  • Vibrio cholerae
  • Escherichia coli
  • Campylobacter jejuni
  • Salmonella spp.
  • Shigella spp
  • Listeria monocytogenes
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7
Q

What are the features of V. cholerae?

A
  • Gram negative
  • Comma-shaped rod
  • Flagellated
  • Charecterised by epidemics and pandemics
  • Human-only pathogen
  • Flourishes in communities with no clean drinking water / sewage disposal
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8
Q

How can V. cholerae be desifered?

A

Based on O antigens

  • O1: Associated with early pandemics
  • Non-O1: 0139 associated with recent outbreaks
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9
Q

What are the 2 types of V. Cholerae vaccines?

A
  • Parenteral vaccine: low protective efficiency

- Oral vaccine: effective and suitable for travellers

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10
Q

How infective is V. Cholera and how does it infect humans?

A
  • Only infective in large doses
  • Many organisms killed in stomach
  • Colonisation of SI involving flagellar motion, mucinase, attachement to specific receptors
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11
Q

How do the V. cholerae cause diarrhoea?

A
  • Produces multicomponent toxin - CTx
  • Causes a massive increase of cAMP opening CFTR
  • Opening CFTR causes Cl- to move out of cell
  • Causes loss of fluid and electrolytes without damage to enterocytes
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12
Q

Describe the Cholera Toxin (CTx)

A
  • Oligomeric complex of 6 protein subunits
    1 copy of A subunit (enzymatic)
    5 copies of B subunit (receptor binding)
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13
Q

How much fluid is lost as a result of cholera infection and what does this result in if untreated?

A
  • 1 litre / hour
  • Electrolyte imbalance leading to dehydration, metabolic acidosis and hypokalemia
  • Hypovolemic shock
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14
Q

What is the mortality rate of cholera infection?

A
  • 40 - 60%

- <1% mortality if given fluid / electrolytes (ORT)

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15
Q

How would you describe stool from a patient with cholera?

A

Rice Water stool - completely fluid, no blood, mucous can be present

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16
Q

Describe the features of E. coli?

A
  • Gram negative
  • Bacilus
  • Member of normal GI microbiota
  • Can be resistant to acid
  • Some strains possess virulence factors enabing them to cause disease
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17
Q

What are the types of E. coli causing GI infections?

A
  • EPEC - enteropathogenic
  • ETEC - enterotoxigenic
  • VTEC/STEC - verocytotoxin-producing
  • EHEC - enterohaemorrhagic
  • EIEC - enteroinvasive
  • EAEC - enteroaggregative
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18
Q

What E. coli strain is known for causing travellers diarrhoea

A

ETEC (occurs in 20 - 50% of travellers)

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19
Q

What E. coli infection has sporadic cases and outbreaks of infection in under 5’s?

A

EPEC

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20
Q

What strain of E.coli is a food-borne infection in areas of poor hygiene?

A

EIEC

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21
Q

What bacteria creates a pedestal formation?

A

E. coli

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22
Q

What is an endotoxin?

A

It is actually part of the bacteria

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23
Q

What is an exotoxin?

A

Secreted by the bacteria

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24
Q

What does the heat-labile (LT) toxin produced by E. coli cause an increase in?

A

cAMP and secretion

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25
Q

What does the heat-stable toxin (STa) produced by E. colicause an increase in?

A

cGMP and secretion

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26
Q

What bacteria is often found in undercooked chickens and the most common cause of diarrhoea in the UK?

A

Campylobacter jejuni

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27
Q

Desribe the features of C. jejuni?

A
  • Gram negative
  • Helical bacillus
  • Large animal reservoir
  • Causes food-associated diarrhoea
  • Mucosal inflammation and fluid secretion
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28
Q

Describe the affect of C. jejuni infection on the SI from a histological point of view?

A
  • Inflammation involves entire mucosa
  • Vilous atrophy
  • Necrotic debris in crypts
  • Thickening of basement membrane
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29
Q

What are the features of Salmonella spp?

A
  • Gram negative

- Bacilli

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30
Q

How many serotypes of Salmonella spp are there?

A

> 2000 serotypes

31
Q

How is Salmonella spp transmitted?

A
  • Consumption of raw / undercooked meat, contaminated eggs and milk
  • Secondary spread can be human-human
  • Ingestion of large numbers of Salmonella to cause infection
32
Q

What are some important Salmonella species?

A
  • S. typhi
  • S. paratyphi
  • S. enteritidis
33
Q

How does salmonella cause diarrhoea?

A
  • Large numbers of salmonella bacteria ingested
  • Absorption to epithelial cells in terminal section of SI
  • Penetration of cells and migration to lamina propria
  • Multiplication in lymphoid follicles
  • Inflammation response mediates release of prostaglandins
  • Stimulation of cAMP
  • Release of fluid and electrolytes causing diarrhoea
34
Q

What cac S. typhus and S. paratyphus cause?

A
  • Enteric fevers: typhoid and paratyphoid
  • Systemic infections initiated in GI tract
  • Restricted to humans
35
Q

What cells do S. typhi and paratyphi bacteria multiply and transport themsleves in?

A

Macrophages

36
Q

How long can S. typhi stay in the stools for in patients with Typhoid fever?

A

Several weeks after recovery

37
Q

How often often can S. typhi become a chronic infection in the body?

A

1-3% of the time, more common in women and the elderly

38
Q

Name a notifiable disease

A

Typhoid fever (S. typhi)

39
Q

What are the spots called that present on those with typhoid fever?

A

Rose spots

40
Q

What are the 2 types of Typhoid vaccines?

A 
- Oral; live attenuated
booster needed after 5 years 
-Parenteral; capsular polysaccharide 
booster after 2 years 
- 50 - 80% effective 
- Recommended for travellers to endemic areas
41
Q

What is the shape of Shigella spp?

A
  • Bacillus
42
Q

What does shigella spp. cause?

A

Shigellosis (bacillary dysentary) spread via human to human

43
Q

What are the 4 species of Shigella spp?

A
  • S. dysenteriae: most serious
  • S. flexneri: sever disease
  • S. boydii: severe disease
  • S. sonnei: mild infections
44
Q

Describe the pathogenesis of Shigella infection?

A
  • Attaches to mucosal epithelium of distal ileum and colon
  • Causes inflammation and ulceration
  • Rarely invasive
  • Produces Shiga toxin (STx)
  • Diarrhoe watery initially, later cacn contain blood and mucous
  • Usually self-limiting
45
Q

Describe the shape of L. monocytogenes

A

Coccobaccillus

46
Q

What does L. monocytogenes cause?

A

Listeriosis usually presents as meningitis

47
Q

How many organisms are needed to cause listeriosis?

A

< 1000

48
Q

What populations are at risk of Listeiosis?

A
  • Pregnant

- Immunosuppressed individuals

49
Q

What causes listeriosis?

A
  • L. monocytogenes

- Can be present in pate, soft cheese, unpasteurised milk, humus

50
Q

Name 3 viruses which can cause diarrhoea

A
  • Rotavirus
  • Noravirus
  • Enteric adenovirus
51
Q

Desribe the structure of rotavirus

A
  • ‘rota’ - wheel

- 11 seperate segments of double-stranded RNA

52
Q

Who is affected by rotavirus?

A
  • Many mammals

- Most common in children < 2 years old

53
Q

How is Rotavirus transmitted?

A
  • Faeco-oral, but may also be faeco-respiratory
  • As few as 10 ingested particles can cause disease
  • It is a seasonal occurance
54
Q

Describe the pathogenesis of rotavirus infection?

A
  • Incubation period of 1-2 days
  • Replication of virus in SI epithelial cells at tips of villi
  • Results in villous atrophy
  • Damage caused to infected cells leaving immature cells with reduced absorptive capacity for sugar, water and electrolytes
  • Onset of vomitting, diarrhoea lasting 4 - 7 days
55
Q

How many rotavirus particles are released per gram of faeces?

A

Up to 10^10 - 10^11

56
Q

What virus causes the majority of sickness and diarrhoea outbreaks worldwide?

A

Norovirus

57
Q

What percentage of adults have had norovirus at some point in their lives?

A

60%

58
Q

How is norovirus transmitted?

A
  • Human only pathogen
  • Transmission is faeco-oral, contaminated water / shellfish, fomites
  • < 100 virons can cause infection
59
Q

What percentage of community-acquired diarrhoeas in young children are caused by enteric adenovirus?

A

10%

60
Q

What is antibiotic-associated diarrhoea?

A
  • Does not involve ingestion of pathogen or toxin

- Can arise from disruption of gut microbiota following antibiotic therapy

61
Q

What bateria can overgrow in the gut as a result of tetracycline antibiotic therapy?

A

Allows colonisation by Staphylococcus aureus and candida sp.

62
Q

What antibiotic suppresses the gut microbiota and allows Clostridium difficile to multiply?

A

Clindamycin

63
Q

C. dificile is now associated with resistance to what antibiotic?

A

Vancomycin

64
Q

How does C. difficle survive harsh conditions?

A

the production of spores - produces an enterotoxin and cytotoxin

65
Q

Desribe the structure of Helicobacter pylori?

A
  • Gram negative
  • Spiral
  • Flagellated
  • Microaerophilic
  • > 80% infected individuals are asymptomatic
66
Q

What diseases can H pylori cause?

A
  • Duodenal ulcers
  • Gastric ulcers
  • GORD
  • Non-ulcer dyspepsia
67
Q

What are the key features of H pylori?

A
  • Acid-inhibiting protein - survival in stomach
  • Urease - neutralisation of acid pH
  • Adhesins - ninding to gastric epithelium
  • Cytotoxin - damage to gastric epithelium
  • Flagellum - movement through gastric mucus layer
68
Q

How is H pylori associated Gastritis treated?

A 
- 1 week (7 days) triple therapy 
EITHER 
- PPI + clarithromycin + amoxycyillin 
OR 
- PPI + clarithromycin + Metronidazole
69
Q

What is food poisoning?

A

Syndrome is restricted to diseases caused by toxins elaborated by contaminating bacteria in food before it is consumed

70
Q

What are examples of toxins?

A
  • Emetic toxins of Bacillus cereus
  • Enterotoxin of Staphylococcus aureus
  • Neurotoxin of Clostridium botulinum
71
Q

What can Bacillus cereus be found in?

A

Rice

72
Q

How does clostridium perfringens cause disease?

A
  • Usually caused by type A strains from animal guts and soil
  • Contamination of raw meat products
  • Spores survives cooking and germination takes place
  • Multiplication in large intestine, production of spore and enterotoxin
  • Damage to intestinal epithelium
  • Diarrhoea
73
Q

What is Oral Rehydration Therapy?

A
  • Involves the replacements of fluids and electrolytes lost during diarrheal illnes
  • 90 - 95% of cases of acute diarrhoea can be successfully treated with an oral rehydration solution (ORS)
  • ORS increases the resorption of fluids and salts into the intestinal wall

MD3002 Pathology (19 decks)

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