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Shigella mahadi ppt Shigella mahadi ppt Presentation Transcript

  • Sharq Elneil CollegeSchool of Medical Laboratory Sciences Department of Microbiology Medical Bacteriology course shigella U.Mahadi Hassan Mahmoud Bsc, Msc, MIBMS Microbiology
  • Kiyoshi Shiga7 February 1871
  • Historical informationDiscovered over 100 years ago by a Japanese scientist named Kiyoshi Shiga,Since its discovery, there have been several epidemics of shigellosis (caused by the S. dysenteriae bacteriumOutbreak in the Mexican-Guatemalan border caused the deaths of 20,000 people
  • Reservoirs:Human intestines are the natural habitat and reservoir for Shigella ,thus the bacteria are present in the stools of an infected person up to a week or two after the alleviation of symptoms
  • Morphology Shigellae are Gram negative, rods.Unlike salmonellae and many otherenterobacteria, shigellae are non-motile. Non-sporing Noncapsulate
  • Medically Important sppSubgroup A: Shigella dysenteriaeContains 12 distinct serotypesSerotype 1 was formerly called S. shigaSerotype 2 was formerly called S. schmitziiSubgroup B: Shigella flexneriContains 6 related serotypes and 4 serotypesdivided into subserotypes.Subgroup C: Shigella boydiiContains 18 distinct serotypesSubgroup D: Shigella sonneiContains one serotype
  • Culture &chaacteristics:Shigellae are aerobes and facultativeanaerobes.They grow between 10–45 ºC with anoptimum temperature of 37 ºC.Specimens must be cultured with theminimum of delay. A selective medium is required toisolate Shigella species from faeces.
  • XLD agar: Shigellae produce red-pinkcolonies, 2–4 mm in diameter,without black centresDCA and MacConkey agar:Shigellaeproduce non-lactose fermenting palecoloured 1–2 mm diameter colonies.On prolonged incubation, S. sonneiforms pink colonies
  • .Salmonella-Shigella (SS) agar: Despite its name, this medium isnot suitable for isolating shigellae asit is inhibitory to most strains
  • Routes of transmissionFaecal-oral route with poor sanitation,unhygienic conditions, overcrowding,facilitating the rapid spread of infection.Only a few organisms are required tocause disease.Houseflies help to transfer shigellaefrom faeces to food. The
  • Reactions of shigellae● Lactose negative (S. sonnei is a late lactose andsucrose fermenter)● H2S negative● Urease negative● Oxidase negative● Citrate negative● Lysine decarboxylase (LDC) negative● Ornithine decarboxylase (ODC) negative exceptS. sonnei which is ODC positive● Beta-galactosidase (ONPG) negative. S. sonneiand up to 15% of Sd 1 strains and minority ofS. boydii strains are ONPG positive
  • Colicins typingColicins are bactericidal macromoleculeswhich have narrow spectrum activity and theyare produced by Sh.sonneii (16)colicins kill sensitive bacteria in 3 definedsteps :1. Adsorption onto a specific receptor at the surface of the bacterium.2. Translocation across the outer membrane.3. Killing activity.
  • Virulence factorsseveral toxins (endotoxin, enterotoxin, andcytotoxin)its ability to induce endocytosis into host cells, andintracellular growth. Each variation of the bacteria is able to penetratelarge intestine epithelial cells and multiply within.S. dysenteriae, however, causes more severesymptoms due to the production of the Shiga toxin.This enables it to kill host cells by inhibiting proteinsynthesis
  • Pathology: ShigellosisDeveloping countries:Sh. flexneri is endemic (always present) in mostcommunitiesSh. dysenteriae type 1 often occurs in an epidemic patternThese two species of Shigella generally produce the mostsevere illness.Developed countries:Sh. sonnei is the most common and is the least virulentSh. boydii causes disease of intermediate severity is leastcommon, except in the Indian sub-continent.
  • Fecal-oral transmissionperson-to-person, fomites, food, water,Waterborne and water-washedInfectious dose: low; as few as 10 cells toinfectIncubation period: 1 to 7 days; typically,1-3 daysDuration of illness: untreated: severe symptoms for about two weeks Antibiotic treatment shortens illness and prevent spread to others
  • Shigellosis - Complicationssevere anorexia (loss of appetite)hypoproteinaemia (a low concentration of blood protein)hyponatraemia (a low concentration of blood sodium)dilation of the large intestineseizuresanaemiakidney damagepersistent diarrhoea
  • Laboratory diagnosisSpecimens:Collection of SpacimenCultureIdentificaionSerologyMolecular characterization -
  • Antimicrobial suseptibility testingAmpicillin,Septra,Nalidixic acidCiprofloxacin. Since manyShigella are becoming resistant to antibiotics, theyshould be avoided as a means of treatment for mildcases , as most will recover without help.
  • Prevention and Control: Handwashing, especially afterdefacationImproved sanitation and hygiene Improve water, wastetreatment/disposal and food sanitation Reduce overcrowding, etc. No effective vaccine