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Shigella

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Bruno Mmassy
Bruno Mmassy

Shigella are Gram-negative bacilli that cause shigellosis (bacillary dysentery) in humans. There are four species (S. dysenteriae, S. flexneri, S. boydii, S. sonnei) which are differentiated based on antigen types. Shigellosis ranges from asymptomatic to severe diarrhea with blood/mucus and is typically transmitted through the fecal-oral route. The bacteria invade the colonic epithelium through attachment and enterotoxins can cause electrolyte/nutrient absorption issues leading to symptoms. Treatment focuses on rehydration while prevention emphasizes water/sewage sanitation and antibiotic treatment of carriers.

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Shigella Dr Sabrina Moyo Department of Microbiology and Immunology
Definition An enterobacteriaceae Gram negative bacilli. Readily growth O2 + An O2. Metabolically active, fermenting a variety of substrates. Mostly non-motile, non sporing, non acid fast, 2-4um x 0.4 -0.6um rounded ends.
Morphology & Physiology    Small Gram-negative, facultatively anaerobic, coliform bacillus    Non-motile (no H antigen)    Possess capsule (K antigen) and O antigen    K antigen not useful in serologic typing, but can interfere with O antigen determination    O antigens : A, B, C, D correspond respectively to the four species    Non-lactose fermenting    Bile salts resistant: trait useful for selective media ferment glucose reduce nitrates (NO 3 to NO 2 or N 2 ) are oxidase negative
Taxonomy Family Enterobacteriaceae Shigella dysenteriae : most serious form of bacillary dysentery Shigella flexneri : shigellosis in underdeveloped countries Shigella sonnei : shigellosis in developed countries Shigella boydii
Taxonomy Classification: 4 groups or species on the based on difference in O antigen and some biochemical reactions Group A - S. dysenteriae 1-10 group B - S. flexneri 1-6 group C - S. boydii 1-15 group D - S. sonnei 1
Clinical Syndromes (Shigellosis)    Ranges from asymptomatic infection to severe bacillary dysentery    Two-stage disease: watery diarrhea changing to dysentery with frequent small stools with blood and mucus, tenesmus , cramps, fever Early stage :    Watery diarrhea attributed to the enterotoxic activity of Shiga toxin    Fever attributed to neurotoxic activity of toxin  
Clinical Syndromes Process involves: 1. Ingestion 2. Non-invasive colonization and cell multiplication 3. Production of the enterotoxin by the pathogenic bacteria in the small intestine;   Second stage :    Adherence to and tissue invasion of large intestine    Typical symptoms of dysentery    Cytotoxic activity of Shiga toxin increases severity
Epidemiology    Shigellosis is a major cause of diarrheal disease (developing nations)    Major cause of bacillary dysentery (severe second stage form of shigellosis)     Leading cause of infant diarrhea and mortality (death) in developing countries
Epidemiology Shigella occurs naturally in higher primates Spread from human to human via the fecal-oral route   Less frequently, transmission by ingestion of contaminated food or water    Outbreaks usually occur in close communities;    Secondary transmission occurs frequently
Epidemiology   Low infectious dose (10 2 -10 4 CFU) with 1-3 day incubation period Carriage of the organism persists for approximately one month following convalescence
Pathogenesis & Immunity Invasiveness involves attachment (adherence) and internalization Controlled by a multi-gene virulence plasmid Organisms penetrate through colonic mucosa invade and multiply in the colonic epithelium Not beyond the epithelium into the lamina propria
Pathogenesis & Immunity   Bacterial cells preferentially attach to and invade into M cells in Peyer's patches of small intestine M cells typically transport foreign antigens from the intestine to underlying macrophages, Shigella can lyse the phagocytic vacuole (phagosome) and replicate in the cytoplasm
Pathogenesis & Immunity Exotoxin (Shiga toxin) is neurotoxic , cytotoxic , and enterotoxic , encoded by chromosomal genes, Enterotoxic effect : Shiga toxin adheres to small intestine receptors Blocks absorption (uptake) of electrolytes, glucose, and amino acids from the intestinal lumen
Pathogenesis & Immunity Cytotoxic effect: B subunit of Shiga toxin binds host cell glycolipid in large intestine , Inactivate the 60S ribosomal subunit, Inhibit protein synthesis, causing cell death, microvasculature damage to the intestine, and hemorrhage (blood and fecal leukocytes in stool)    Neurotoxic effect: Fever, abdominal cramping are considered signs of neurotoxicity
Laboratory Identification : Closely related to Escherichia Species (serogrouping and biochemical analysis Stool specimens and rectal swabs should be cultured soon after collection or placed in appropriate transport medium ( Cary-Blair medium) Readily isolated on selective/differential agar media ( XLD , SS , and brilliant green agar Lactose nonfermenter
Treatment, Prevention & Control : Dehydration is problem to attend Treat carriers, major source of organisms; Cirpflxacin , Erythromycin Antibiotic resistance is a major problem Proper sewage disposal and water chlorination Oral vaccines of Shigella : E. coli hybrids or Shigella mutants offers immunity for six months to one year
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Shigella

  • 1. Shigella Dr Sabrina Moyo Department of Microbiology and Immunology
  • 2. Definition An enterobacteriaceae Gram negative bacilli. Readily growth O2 + An O2. Metabolically active, fermenting a variety of substrates. Mostly non-motile, non sporing, non acid fast, 2-4um x 0.4 -0.6um rounded ends.
  • 3. Morphology & Physiology    Small Gram-negative, facultatively anaerobic, coliform bacillus    Non-motile (no H antigen)    Possess capsule (K antigen) and O antigen    K antigen not useful in serologic typing, but can interfere with O antigen determination    O antigens : A, B, C, D correspond respectively to the four species    Non-lactose fermenting    Bile salts resistant: trait useful for selective media ferment glucose reduce nitrates (NO 3 to NO 2 or N 2 ) are oxidase negative
  • 4. Taxonomy Family Enterobacteriaceae Shigella dysenteriae : most serious form of bacillary dysentery Shigella flexneri : shigellosis in underdeveloped countries Shigella sonnei : shigellosis in developed countries Shigella boydii
  • 5. Taxonomy Classification: 4 groups or species on the based on difference in O antigen and some biochemical reactions Group A - S. dysenteriae 1-10 group B - S. flexneri 1-6 group C - S. boydii 1-15 group D - S. sonnei 1
  • 6. Clinical Syndromes (Shigellosis)    Ranges from asymptomatic infection to severe bacillary dysentery    Two-stage disease: watery diarrhea changing to dysentery with frequent small stools with blood and mucus, tenesmus , cramps, fever Early stage :    Watery diarrhea attributed to the enterotoxic activity of Shiga toxin    Fever attributed to neurotoxic activity of toxin  
  • 7. Clinical Syndromes Process involves: 1. Ingestion 2. Non-invasive colonization and cell multiplication 3. Production of the enterotoxin by the pathogenic bacteria in the small intestine;   Second stage :    Adherence to and tissue invasion of large intestine    Typical symptoms of dysentery    Cytotoxic activity of Shiga toxin increases severity
  • 8. Epidemiology    Shigellosis is a major cause of diarrheal disease (developing nations)    Major cause of bacillary dysentery (severe second stage form of shigellosis)     Leading cause of infant diarrhea and mortality (death) in developing countries
  • 9. Epidemiology Shigella occurs naturally in higher primates Spread from human to human via the fecal-oral route   Less frequently, transmission by ingestion of contaminated food or water    Outbreaks usually occur in close communities;    Secondary transmission occurs frequently
  • 10. Epidemiology   Low infectious dose (10 2 -10 4 CFU) with 1-3 day incubation period Carriage of the organism persists for approximately one month following convalescence
  • 11. Pathogenesis & Immunity Invasiveness involves attachment (adherence) and internalization Controlled by a multi-gene virulence plasmid Organisms penetrate through colonic mucosa invade and multiply in the colonic epithelium Not beyond the epithelium into the lamina propria
  • 12. Pathogenesis & Immunity   Bacterial cells preferentially attach to and invade into M cells in Peyer's patches of small intestine M cells typically transport foreign antigens from the intestine to underlying macrophages, Shigella can lyse the phagocytic vacuole (phagosome) and replicate in the cytoplasm
  • 13. Pathogenesis & Immunity Exotoxin (Shiga toxin) is neurotoxic , cytotoxic , and enterotoxic , encoded by chromosomal genes, Enterotoxic effect : Shiga toxin adheres to small intestine receptors Blocks absorption (uptake) of electrolytes, glucose, and amino acids from the intestinal lumen
  • 14. Pathogenesis & Immunity Cytotoxic effect: B subunit of Shiga toxin binds host cell glycolipid in large intestine , Inactivate the 60S ribosomal subunit, Inhibit protein synthesis, causing cell death, microvasculature damage to the intestine, and hemorrhage (blood and fecal leukocytes in stool)    Neurotoxic effect: Fever, abdominal cramping are considered signs of neurotoxicity
  • 15. Laboratory Identification : Closely related to Escherichia Species (serogrouping and biochemical analysis Stool specimens and rectal swabs should be cultured soon after collection or placed in appropriate transport medium ( Cary-Blair medium) Readily isolated on selective/differential agar media ( XLD , SS , and brilliant green agar Lactose nonfermenter
  • 16. Treatment, Prevention & Control : Dehydration is problem to attend Treat carriers, major source of organisms; Cirpflxacin , Erythromycin Antibiotic resistance is a major problem Proper sewage disposal and water chlorination Oral vaccines of Shigella : E. coli hybrids or Shigella mutants offers immunity for six months to one year