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Shigella.ppt
Shigella is a genus that primarily infects the human intestine and causes bacillary dysentery or shigellosis, characterized by bloody, mucopurulent stools. The species include Shigella dysenteriae, Shigella flexneri, Shigella boydii, and Shigella sonnei, with varying virulence and cultural characteristics. Diagnosis involves stool culture, while treatment typically requires rehydration and antibiotics based on strain sensitivity, with preventive measures focused on hygiene and food safety.
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Shigella.ppt
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- 2. INTRODUCTION • The genusShigella exclusively infects human intestine. • Shigella dysenteriae is the causative agent of bacillary dysentery or shigellosis in humans. • It is a diarrheal illness which is characterized by frequent passage of blood stained mucopurulent stools. • The four important species of the genus Shigella are: – Shigella dysenteriae – Shigella flexneri – Shigella sonnei – Shigella boydii.
- 3. MORPHOLOGY • Short GNB •1-3 μm x 0.5 μm • Nonmotile • Noncapsulate & nonsporing • Fimbriae – may be present
- 4. CULTURAL CHARACTERISTICS Facultativeanaerobes pH 7.4 Temp – 100 -400 C Grow on ordinary media Colonies: small, <2 mm; circular, convex smooth & translucent MacConkey Agar, Salmonella-Shigella agar& DCA: colourless (except Sh sonnei) Wilson & Blair BS medium: growth inhibited
- 6. RESISTANCE • 56oC X1 hour • 1% phenol X 30 mins • Water & ice 1-6 months • 1-6 weeks on dried stools • Acidic stools – few hours • Antibiotics: multiple resistance- streptomycin, ampicillin, chloramphenicol
- 7. BIOCHEMICAL CHARACTERISTICS • Nonlactose fermenter (Sh sonnei- late) • MR + • Mannitol : Subgroup A –ve, Rest +ve • Sucrose & H2S –ve • Indole : S. dysentriae serotype 2 +, S flexneri serotype 6, S sonnei ALWAYS NEGATIVE • Catalase -ve Sh dysentriae type 1, Sh flexneri 4a
- 8. CLASSIFICATION • Shigella areclassified into four Subgroups/ species based on biochemical and Serological characteristics: – Subgroup A: Shigella dysentriae – Subgroup B: Shigella flexneri – Subgroup C: Shigella boydii – Subgroup D: Shigella sonnei
- 9. Subgroup A Sh.dysentriae • 12serotypes, mannitol -ve • Type 1- Sh.shiga (Shiga’s bacillus) – Most virulent – Catalase –ve – Indole –ve – Produces exotoxins: Enterotoxins, Neurotoxin, cytotoxin • Type 2 –Sh. smitzi- Indole +ve • Type 3-7 Large Sach’s group
- 10. Subgroup B Sh.flexneri • Mostcommon in India • 6 serotypes • Mannitol +ve • Biochemically and antigenically heterogenous
- 11. Subgroup C Sh. boydii •Least common • Biochemically similar to Sh. Flexneri • 15 serotypes • Mannitol +ve
- 12. Subgroup D Sh. sonnei •Least virulent • Late lactose and sucrose fermenter • Most common species in West • Indole –ve • Antigens – 2 phases (I & II) • Two different colony morphotypes • Subclassified into 17 colicine types
- 14. VIRULENCE FACTORS • Shigelladysenteriae produces 3 types of toxins: –Endotoxin –Exotoxin –Verocytotoxin.
- 15. Various toxins ofShigella Toxins Mode of Action Endotoxin It is released after autolysis, it has irritating effect on intestinal wall which causes diarrohea and intestinal ulcers Exotoxins It is a powerful toxin and acts as well as neurotoxin. As Entertoxin: it induces fluid accumulation. As Neurotoxin: it damages the endothelial cells of small blood vessels of CNS which results in coma and death. Vero cytotoxin It acts on vero cells
- 16. PATHOGENESIS • Infective doseis low 10 - 100 bacilli • Source of Infection – Patient or carriers • Route of entry – faecal – oral route • Site of infection – Large intestine Incubation Period – Less than 48 hours (1–7 days) • Mode of transmission – Food, finger, faeces and flies
- 17. Sh. Dysenteriae causesbacillary dysentery. The pathogen enters into the host by the ingestion of contaminated food The bacilli reaches large intestines and adheres to the epithelial cells of villi. Multiples and produces toxins. Which stimulates an inflammatory reaction and causes extensive tissue destruction. Which leads to necrosis of epithelial cells. The necrosed epithelial, becomes soft and friable and leads to ulcers. Abdominal cramps and pain are caused by the distruption of the intestine. The degeneration of intestinal villi and local erosion causes bleeding, heavy mucous secretion resulting in BACILLARY DYSENTERY.
- 20. CLINICAL MANIFESATION • Frequentpassage of loose, scanty faeces containing blood and mucus. • Abdominal cramps and tenesmus (straining to defecate). • Fever and vomiting. • Hemolytic uremic syndrome (It is a condition caused by the abnormal destruction of red blood cells).
- 21. LAB DIAGNOSIS • Specimens:Fresh stool is collected. • Direct Microscopy: Saline and Lugol’s iodine preparation of faeces show large number of pus cells, and erythrocytes. • Culture: For inoculation, it is best to use mucus flakes (if present in the specimen) on MacConkey agar and SS agar. After overnight incubation at 37°C, the plates are observed for characteristic colonies, which is confirmed by Grams staining and biochemical reactions.
- 22. • Serotyping: Identificationconfirmed by slide agglutination with polyvalent & monovalent sera. Tube agglutination if doubtful. Boil 1hr x 100o C and look for agglutination if masking K Ag present. Tube Agg- in saline Mercuric iodide soln (Mackie McCartney) • Serology for epidemeology
- 23. • DNA ColonyHybridization – DNA probe directed against various plasmid- encoded virulence genes • PCR- Primer directed against plasmid- encoded virulence gene. Problems: living vs. dead cells, plasmid stability • Latex particle agglutination - clinical samples • ELISA - clinical samples
- 24. TREATMENT AND PREVENTION •Uncomplicated shigellosis is a self – limiting condition that usually recovers spontaneously. • In acute cases, oral rehydration therapy (ORT) is done. • In all severe cases, the choice of antibiotic should be based on the sensitivity of prevailing strain. • Many strains are sensitive to Nalidixic acid and Norfloxacin.
- 25. • The precautionsfor Shigella are same as that of any food and water-borne diseases. • WASH YOUR HANDS thoroughly before and after a meal. • Wash your hands properly after a bowel movement. • Ensure the water that you drink is clean and the fruits and vegetables are fresh. • Ensure products such as milk, chicken, and fish that have a higher tendency to spoil must be kept at a proper temperature and also cooked well
- 26. When to suspectfor Shigella??? • A person who has severe diarrhoea, which means 20 or more bowel movements in a day, A patient with mild diarrhoea may wait. • If child develops bloody diarrhoea or diarrhoea severe enough to cause weight loss and dehydration. • If the infected person is running a fever of 101 degree F (38ᵒC) or higher.