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Block 4 > 7.2 Pathogenesis of Infectious Diarrhoea > Flashcards

7.2 Pathogenesis of Infectious Diarrhoea Flashcards

1
Q

define secretory diarrhoea and what causes it?

A

Increased secretion or decreased absorption of fluids and electrolytes

Vibrio cholera, C.difficile, ETEC

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2
Q

Define osmotic diarrhoea and what causes it?

A

Through loss of absorptive surface causing increased osmolarity of intestinal contents and malabsorption

EHEC

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3
Q

Define inflammatory diarrhoea and what causes it?

A

Through inflammation causing increased damage to host tissues resulting in fluid exudation

C.Difficile

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4
Q

What are the advantages of an intracellular lifestyle?

A

Access to nutrients
Escape from host defences
Protection from antibiotics

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5
Q

What do intracellular infections require and how do they do it?

A

Invasion - gain access to epithelial cells via M cells

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6
Q

What are examples of intracellular enteric pathogens?

A 
Shigella 
Enteroinvasive E.Coli 
Nontyphoidal salmonella 
Typhoidal salmonella 
Campylobacter 
Listeria monocytogenes
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7
Q

What are the characteristics of inflammatory diarrhoea?

A

presence of fever and polymorphneucleotides in stool

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8
Q

How do PMNs regulate absorption?

A

through cytokine secretion and through secretion of a precursor to adenosine that activates CFTR promoting Cl secretion

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9
Q

What distinguishes shigella from salmonella?

A

Shigella cannot ferment xylose (XLD agar)

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10
Q

What is the spread of shigella?

A

fecal-oral

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11
Q

What are the 4 types of shigella species?

A

Shigella sonnei, Shigella flexneri and boydii, Shigella dysenteriae (most severe)

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12
Q

What are the symptoms of shigellosis?

A

Fever, abdominal cramps, severe and bloody diarrhoea often with pus (PMNs) and mucus

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13
Q

What types of diarrhoea does shigellosis cause and why?

A

Inflammatory - due to invasion
Osmotic - loss of absorptive surface
Secretory - shigella enterotoxins

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14
Q

What are the virulence stratagies of shigella?

A
  1. Invasiveness
  2. AB5 exotoxin (shiga toxin)
  3. IcsA autotransporter responsible for intercellular spread (avirulent without)
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15
Q

What type of secretion system is shigella?

A

Type 3

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16
Q

How does shigella cause infection?

A

makes way from apical to basolateral side where it is taken up by macrophages. This causes apoptosis of the macrophage allowing the toxin to replicate in the cytoplasm and infect and invade adjacent cells (with the actin comet tail propelling the shigella)

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17
Q

What are the properties of Enteroinvasive E.Coli?

A

The same as Shigella (can only be differentiated with serine, xylose and/or sodium acetate and mucate fermentation)

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18
Q

What kind of pathogen is Salmonella?

A

Motile, gram negative rods, facultative anaerobe resistant to bile salts

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19
Q

What kind of pathogen is shigella?

A

non motile, gram negative rods, facultative anaerobes resistant to gastric acid and bile salts

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20
Q

What are the two species of salmonella

A

Bongori and enterica

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21
Q

what is the major pathogenic strain of salmonella?

A

Salmonella enterics serovar Typhimurium

22
Q

What are the classifications of salmonella and which strains usually cause them ?

A

Non typhoidal - cause gastritis (S.enterica serovar Typhimurium and Enteritidis)

Typhoidal - cause enteric (thyphoid/paratyphoid) fever (S.enterica serovar Typhi and Paratyphi)

23
Q

What is the incubation of Salmonellosis - gastro ?

A

2-7 days with duration 2-7 days

24
Q

What are the symptoms of salmonellosis - gastro?

A

vomiting, fever, abdominal cramps, watery diarrhoea with PMNs

25
Q

What type(s) of diarrhoea is caused by salmonella?

A

all 3

26
Q

What is the treatment for salmonella?

A

Usually self limiting unless extraintestinal disease develop, sever colitis, infants or immunosuppressed individuals infected

27
Q

what is the common cause of non-tyhpoidal salmonella?

A

Poultry and eggs

28
Q

What are the symptoms of enteric salmonellosis?

A

fever, vomiting, abdominal cramps, diarrhoea with PMNs, headache, nausea, rash of rose-coloured spots

29
Q

what is the incubation of enteric salmonellosis?

A

7-28 days (typhi) 1-15 days (paratyphi)

30
Q

What is the spread of enteric salmonellosis?

A

fecal-oral

31
Q

What is the treatment of typhoidal salmonellosis?

A

Antibiotics
Identify and treat carriers
Removal of gallbladder if antibiotics fail

32
Q

What are the strains of salmonella that cause enteric infection?

A

S.enterica serovar Typhi and Paratyphi

33
Q

What are the salmonella virulence strategies?

A

Invasiveness
SPI-1 effector protein for invasion into intestinal epithelium
SPI-2 effector proteins required for replication in intestinal epithelium and macrophages
LT-like toxin
Capsule (S.enterica. serovar Typhi only)

34
Q

How does salmonella cause systemic infection?

A

organism consumed
Exit the small intestine via M cells
Taken up by macrophages
Migrate to the mesenteric lymph nodes and multiply
Released into the bloodstream
Remove from blood by macrophages in spleen, bone marrow, liver where they will then multiply and re-enter the blood stream
re-enter the GIT via gallbladder causing inflammation, ulceration and necrosis

35
Q

What type of pathogen is campylobacter?

A

motile gram negative comme shaped rod

36
Q

What are the two strains of campylobacter that commonly cause GIT infections?

A

jejuni and coli

37
Q

what does campylobacteriosis cause?

A

Gastroenteritis - can lead to Guillian-Barre

38
Q

What is the incubation period and duration of campylobacter infection?

A

2-11 days incubation, 3days to 3 week duration

39
Q

What are the symptoms of campylobacter infection?

A

Abdominal cramps, fever, bloody diarrhoea (+ PMNs)

40
Q

What are the common sources of campylobacter infection?

A

Chickens and other animal (contaminated chicken and unpasteurised milk)

41
Q

What is the inflammatory mechanism of campylobacter?

A

invasion of the intestinal epithelium with M cell uptake and with production of bloody diarrhoea

42
Q

What are the virulence factors of campylobacter?

A

Capsule
Lipooligosaccharide require for adherence and invasion
Flagellum

43
Q

What kind of pathogen is Listeria monocytogenes?

A

Motile, gram positive rod

44
Q

What foods are associated with Listeria monocytogenes infection?

A

unpasteurised milk, soft serve ice cream, raw vegetables, cold deli meats, raw seafood

45
Q

Who does Listeria monocytogenes normally infect?

A

immunocompromised, pregnant women and the elderly

46
Q

what are the symptoms of Listeriosis

A

In healthy adults it is asymptomatic

can cause flu like symptoms of gastroenteritis

In immunocompromised can infect any organ but most commonly meningitis

47
Q

What is special about Listeria monocytogenes?

A

Can cross both the placenta and blood brain barrier

48
Q

What is the treatment for Listeria monocytogenes?

A

Ampicillin combined with gentamicin

49
Q

What are the important virulence strategis of Listeria monocytogenes?

A

Listeriolyson O - bacterial escape from vacuole after invasion

ActA responsible for intercellular spread

50
Q

How does Listeria monocytogenes cause infection?

A

After cellular invasion of M cells, Listeria monocytogenes escapes from the vacuole following membrane rupture mediated by Listeriolysin O. It then moves thorugh cytoplasm and then from cell to cell in an actin dependent process.

51
Q

What are the most common infections in Australia?

A

campylobacter > salmonella > EHEC > Listeria

Block 4 (36 decks)

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