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Enterobactericeae genus shigella
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Explore the four main species—Shigella dysenteriae, Shigella flexneri, Shigella boydii, and Shigella sonnei—along with their unique characteristics. Learn about the transmission routes of Shigella, highlighting its infectious nature and public health significance. Understand how Shigella ...

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  • October 21, 2024
  • 2
  • 2020/2021
  • Lecture notes
  • Alison cottell
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Enterobacteriaceae: Genus - Shigella
27 October 2020 22:15

The Enterobacteriaceae: Genus - Shigella
Genus - Shigella
Genetic features:
• 4 Shigella species (based on serological typing)
A: S.dysenteriae- most severe, (ancient) cause of epidemics
B: S. flexneri - most frequent, 60% cases in developed world
C: S. boydii - confined to Indian sub-continent
D: S. sonnei- mildest infection, developed world (main species)

Phylogenetic typing (16s rRNA) now shows that Shigella app. and E. coli are one species but the
distinction status remains to avoid confusion.
○ 4.5 Mb genome, including large virulence plasmid (200kbp) which encodes type 3 secretion
system and key invasion factors located on a plasmid.
○ Average Guanine and Cytosine (G+C) content is 49.6%

Differences between E.coli and Shigella spp.
E.coli:
- Lactose positive
- Ferment glucose (may or may not produce gas)
- Motile
- Decarboxylate lysine
Shigella spp.:
- Lactose negative
- Anaerogenic (does not produce gas)
- Non-motile
- Cannot decarboxylate lysine
E.coli and Shigella spp. can be differentiated on basis of biochemical/morphological tests.

Shigella transmission and disease:
Shigella is a human-only pathogen.
Transmits by faecal-oral route and person-person spread.

Shigellosis (dysentery) - clinical presentation of Shigella infection:
• Aggressively watery or mucoid/bloody diarrhoea, fever, stomach cramps.
• Begins 1-2 days after ingestion of organism and in immunocompetent individuals will resolve
in 5-7 days.
• Affects mostly children under age of 5 years old.
• Low infectious dose (10-100 organisms)
Route of transmission:
○ Faecal shedding and contamination of water and foods
○ Ingestion of food/water with Shigella 10-100 cells
○ Invasion of colonic mucosal cells
○ Inflammation tissue damage
○ Mucoid, purulent bloody diarrhoea-dysentery

Shigella spp. Disease impact:
More than 190 million cases of shigellosis annually worldwide, causing at least 70,000 deaths.
Current global epidemiological burden for shigellosis is attributes to S. flexneri and S. sonnei.

Shigella is able to induce sustained transmissions in close contact communities:
e.g. Orthodox Jewish communities in UK
e.g. Men who have sex with men (MSM community)



E-Shigella Page 1

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