Shigella

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Shigella
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General Characteristics of Shigella

• Coliform bacilli (enteric rods)
• Non motile gram-negative.
• Facultative anaerobes
• Non-lactose fermenting
• Resistant to bile salts
• Four species
• Shigella sonnei (most common in industrial world)
• Shigella flexneri (most common in developing
  countries)
• Shigella boydii
• Shigella dysenteriae

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Clinical Syndromes of Shigella

• Shigellosis bacillary dysentery
• Low infectious dose (102-104 CFU)
• Humans are only reservoir
• Transmission by fecal-oral route
• Incubation period 1-3 days
• Watery diarrhea with fever changing to dysentery
• Leading cause of infant diarrhea and mortality
  (death) in developing countries

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Pathogenesis and Virulence Factors (cont.)

• Virulence attributable to
• Invasiveness
• Attachment (adherence) and internalization
• Exotoxin (Shiga toxin)
• Enterotoxic, neurotoxic and cytotoxic
• Intracellular survival multiplication

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• DEFINITIONS
• Dysentery inflammation of intestines
  (especially of the large intestine - the colon
  (colitis)) with accompanying severe abdominal
  cramps, tenesmus (straining to defecate), and
  frequent, low-volume stools containing blood,
  mucus, and fecal leukocytes (PMNs)
• Bacillary dysentery dysentery caused by
  bacterial infection with invasion of host
  cells/tissues and/or production of exotoxins

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Pathogenesis of Shigella

• Shigellosis
• Two-stage disease
• Early stage (enterotoxic neurotoxic activity )
• Watery diarrhea attributed to the enterotoxic
  activity of Shiga in the small intestine.
• Fever attributed to neurotoxic activity of toxin
• Second stage (Invasion and Cytotoxic activity )
• Due to invasion of large intestine with typical
  symptoms of dysentery
• Cytotoxic activity of Shiga toxin increases
  severity

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Lab Diagnosis

• Specimen
• STOOL
• RECTAL SWAB
• Microscopy
• Non Lact F G ve bacilli
• Non motile non sporing
• Culture
• Salmonella - Shigella Agar
• TIR agar
• Serology Agglutination test- serotyping

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Treatment

• Ampicillin
• Tetracycline
• Ciprofloxacin

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Epidemiology of Shigella Infection
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