1 / 18

Shigella

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.

daria-fleming
Download Presentation

Shigella

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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 x0.4 -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 (NO3 to NO2 or N2) 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. boydii1-15 • 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 (102-104 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 colonicmucosa • 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

  17. THANK YOU!

  18. Reference: www.Slideshare.com

More Related