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Microbiology > 10. Salmonella > Flashcards

10. Salmonella Flashcards

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Biology 101 flashcards
1
Q

What 2 species are 90% related to E.coli?

A

Shigella & Salmonella

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2
Q

What diseases does Salmonella spp. cause?

A

Food poisoning, typhoid

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3
Q

How does Salmonella cause disease?

A

Invasion, localised or systemic, T3SS

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4
Q

Features of Salmonella?

A
  • Highly related (90%) to E. coli
  • Gram neg
  • Motile
  • Facultative
  • Also fairly related to Shigella
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5
Q

Which type of Salmonella covers all the traditional species?

A

Salmonella enterica

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6
Q

What is the most common strain of Salmonella in developed countries?

A

Salmonella enterica Serovar Enteritidis

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7
Q

What condition does S. enterica cause?

A

Gastroenteritis (Salmonellosis)

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8
Q

What are the symptoms of salmonellosis?

A

Nausea, vomiting, pain, diarrhoea, fever

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9
Q

Salmonella is a leading cause of foodborne disease - 2nd only in Western World to?

A

Campylobacter

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10
Q

What food is Salmonella particularly associated with?

A

Poultry & eggs

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11
Q

Classification of Salmonella?

A

> 2,500 serovars (based on O and H antigens)

1,500 in S. enterica enterica

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12
Q

2 types of Salmonella enterica?

A

Typhoidal and non-typhoidal

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13
Q

2 types of typhoidal Salmonella?

A

S. typhi and S. paratyphi

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14
Q

2 types of non-typhoidal Salmonella?

A

S. typhimurium and S. enteritidis

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15
Q

What disease does typhoidal Salmonella cause?

A

Typhoid & paratyphoid fevers (humans)

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16
Q

What disease does non-typhoidal Salmonella cause?

A

Gastroenteritis & extraintestinal (humans & animals)

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17
Q

Most foodborne salmonellosis results in?

A

Gastroenteritis

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18
Q

Spectrum of diarrhoea in gastroenteritis from?

A

from watery to dysentery (blood & mucus in diarrhoea - severe)

19
Q

True or False: Gastroenteritis infection is most often self-limited (non-invasive)

A

True

20
Q

Is S. enteritidis important in causing foodborne outbreaks in developed or developing countries?

A

Developed

21
Q

What causes typhoid (enteric) fever?

A

S. typhi

22
Q

What new disease is emerging from S. typhimurium?

A

Invasive non-typhoidal salmonellosis

particularly in sub-Saharan Africa, predisposed by co-infection i.e. HIV, malaria

23
Q

What are pathogenicity islands?

A

Mobile regions of DNA that have been acquired by bacteria and generally encode virulence factors

24
Q

What is Salmonella typhimurium distinguished by on its genome?

A

Pathogenicity islands

25
Q

What are the 2 Salmonella pathogenicity islands?

A

SPI1 and SPI2 - both encode T3SS (secrete different effector proteins)

26
Q

When is SPI1 involved?

A

More involved earlier on (invasion)

27
Q

When does SPI2 function?

A

After the cells have invaded and are found inside the target cell.
SPI2 becomes more dominant in systemic spread and later stages

28
Q

Pathogenesis of invasive disease (S. enterica typhimurium)?

A
  • Infect epithelial cells of SI
  • Get a ‘splash effect’ due to rearrangement of actin within host cell
  • T3SS: SPI1
  • Grow within vesicle (Salmonella-containing vacuole), do not enter cytoplasm
  • Apoptosis of epithelial cells
  • Virulence plasmids involved
29
Q

True or False: Salmonella is restricted in Salmonella-containing vacuole

A

True. Listeria and Shigella both rupture vacuole membrane. Salmonella in SCV → host cell eventually dies → apoptosis occurs → bacteria released

30
Q

Salmonella entry into host cells is mediated by?

A

SPI1 T3SS and its effectors

31
Q

What is a unique characteristic of Salmonella pathogenesis?

A

Splash effect

32
Q

Histopathology of S. enteritidis?

A

Denuded epithelium & destruction of villi. This damage attracts inflammatory cells. Salmonella will eventually kill epithelial cell, which contributes to gastroenteritis

33
Q

What is the role of the T3SS encoded by SPI2?

A

Bacteria inject proteins into macrophage cytosol → phagosome doesn’t develop normally but instead forms SCV - a privileged and nutrition-rich niche. This facilitates spread as macrophages move on to liver/spleen/LNs throughout the body. Eventually macrophages die, allowing Salmonella to invade other tissues (dissemination) → systemic disease

34
Q

The plasmid involved in virulence (pSLT) encodes what locus?

A

spvRABCD locus - encodes SpvB:ADP-ribosylating toxin - requires SPI2 T3SS. Associated with non-typhoidal salmonellosis

35
Q

Virulence factors in Salmonella?

A
  1. SPIs (SPI1 & SPI2 best studied)
  2. Plasmid (spv locus)
  3. Adhesins
  4. Flagella and chemotaxis
  5. LPS (contributes to inflammation which results in tetrathionate production)
36
Q

What genes does SPI2 encode?

A

ttrRSBCA genes - allow use of tetrathionate reduction as a terminal electron acceptor, which allows Salmonella to respire in the gut (unusual because bacteria usually ferment in stomach)

37
Q

What genes allow Salmonella to respire in the gut, and how?

A

ttrRSBCA genes - allow use of tetrathionate reduction as a terminal electron acceptor

38
Q

S. typhi causes typhoid fever. What are the associated symptoms?

A

High fever, flushed appearance, chills, convulsions, delirium

39
Q

How can survivors of typhoid fever excrete the organism for prolonged periods?

A

Bacteria create a reservoir in the gallbladder - excrete continuously in faeces

40
Q

Pathogenesis of typhoid fever?

A

S. typhi cells enter the blood stream via M cells, multiply in the liver & spleen, and then re-enter the blood in high numbers

41
Q

What is the main difference between S. typhimurium and S. typhi?

A

S. typhimurium enters via macrophages, S. typhi enters via M cells

42
Q

Virulence factors of S. typhi?

A 
Thought to be extremely complicated (as many as 200 genes)
Vi antigen (survival in macrophages, serum resistance)
Typhoid toxin (atypical A-B toxin, only produced in SCV)
43
Q

Treatment for Salmonella infection?

A

Antibiotics contraindicated for salmonellosis, essential for typhoid.
Can also have gallbladder surgery in long-term carriers of S. typhi

44
Q

Why are antibiotics contraindicated for Salmonellosis?

A

Antibiotics release LPS from dying Salmonella cells, inducing severe fever/shock

Microbiology (13 decks)

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