Shigella

• What is the hierarchical classification of Shigella?

  • Domain: Bacteria
  • Phylum: Proteobacteria
  • Class: Gammaproteobacteria
  • Order: Enterobacteriales
  • Family: Enterobacteriaceae
  • Tribe: Escherichieae
  • Genus: Shigella
  • Species: dysenteriae, flexneri, boydii, sonnei
• How many species are there in the genus Shigella?

  Four species
• How is Shigella identified in the clinical laboratory?

  By slide agglutination using commercially available, absorbed rabbit antisera.
• What is the primary reservoir of Shigella species?

  Humans
• How is Shigella transmitted in developing countries?

  Through direct faecal-oral contamination from infected individuals.
• What role do flies play in the transmission of Shigella?

  Flies may contribute to the spread from faeces to food.
• Which species of Shigella are the most virulent?

  1. dysenteriae and S. flexneri
• How are outbreaks of Shigella transmitted in developed countries?

  By uncooked food or contaminated water.
• In which environments can direct faecal-oral spread of Shigella occur?

  In institutional environments such as child day-care centers, mental hospitals, and nursing homes.
• What is the morphology of Shigella bacteria?

  Gram-negative short rods, non-motile, non-flagellated.
• What are the growth requirements for Shigella?

  Aerobic and facultatively anaerobic, non-lactose fermenters, resistant to bile salts.
• What are the suitable media for the growth of Shigella organisms?

  • Nutrient agar
  • MacConkey agar
  • Desoxycholate agar (DCA)
  • Xylose Lysine Deoxycholate (XLD) agar
  • Salmonella-Shigella agar (SSA)
• How do colonies of Shigella appear on MacConkey agar?

  Pale colonies
• What is the biochemical characteristic of all Shigella strains regarding oxidase?

  All strains of Shigella are oxidase negative.
• What do all Shigella species ferment?

  All ferment glucose but do not ferment lactose.
• What distinguishes Shigella from Escherichia coli?

  Shigella is non-motile and usually non-lactose fermenters.
• Who isolated the first member of Shigella and when?

  Kiyoshi Shiga in 1886
• How are Shigella serotypes distinguished?

  By serologic similarity and fermentation reactions.
• What does the term 'dysentery' refer to?

  A condition characterized by frequent passage of stool containing blood and mucus.
• What are the groups of Shigella species and their serotypes?

  • Group A: S. dysenteriae (15 serotypes)
  • Group B: S. flexneri (6 serotypes)
  • Group C: S. boydii (20 serotypes)
  • Group D: S. sonnei (1 serotype)
• What differentiates S. sonnei from other serogroups?

  Positive β-D-galactosidase and ornithine decarboxylase biochemical reactions.
• What is unique about S. dysenteriae serotype 1?

  It produces the Shiga toxin.
• What is the function of the Shiga toxin?

  It inhibits protein synthesis in susceptible mammalian cells.
• What are the major virulence factors of Shigella?

  The toxins produced by the genus, including Shiga toxin.
• What are the modes of transmission for Shigella?

  • Faeces contaminating fingers
  • Contaminated food and water
  • Flies
  • Formites (inert surfaces)
  • Sexual contact (homosexuals)
• What toxin is notably produced by Shigella?

  Shiga toxin
• What are the major virulence factors of Shigella?

  The major virulence factors are the toxins produced by this genus.
• How many types of toxins does Shigella produce?

  Three types of toxins
• What is the role of endotoxin produced by Shigella?

  It increases the motility of the intestine.
• Which type of Shigella produces exotoxin?

  Shigella dysenteriae type 1
• What is another name for Shiga toxin?

  Verocytotoxin
• What is Verocytotoxin also known as?

  Shiga-like toxin
• What are the subunits of VT1 in Verocytotoxin?

  VT1 has two subunits A and B.
• What does subunit A of VT1 do?

  It inhibits protein synthesis.
• What does subunit B of VT1 do?

  It is responsible for toxin binding to susceptible cells.
• What is the mode of transmission for Shigella known as the 4Fs?

  Feces, fingers, food, and flies
• What is the minimum infective dose of Shigella?

  10-100 bacilli
• What are the two stages of Shigella disease?

  Early stage with watery diarrhea and second stage with dysentery.
• What causes the watery diarrhea in the early stage of Shigella infection?

  Enterotoxic activity of Shiga toxin.
• What are the characteristic symptoms of the second stage of Shigella infection?

  Adherence to and tissue invasion of the large intestine.