Diphtheria - Prac. Microbiology


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Diphtheria - Prac. Microbiology

  1. 1. Gram positive bacilli Non-spore forming - Corynebacterium - Listeria Spore- forming - Bacillus - Clostridium
  2. 2. Non-spore forming Corynebacterium
  3. 3. Corynebacterium  Some species are part of normal flora of skin and mm.  Medically important species is Corynebacterium diphtheriae
  4. 4. Morphology  Gram-positive bacilli  Club-shaped  Arranged at acute angles or parallel to each other (Chinese letters).  Meta-chromatic granules.  Non-spore forming
  5. 5. Methylene blue stain: Beaded appearance
  6. 6. Culture Characters  Aerobic.  Growth on: 1. Blood agar 2. Loeffler’s serum: Best morphology 3. Blood tellurite agar: Selective & differential Grey to black colonies
  7. 7. Virulence factors Diphtheria ExotoxinDiphtheria Exotoxin Exotoxin is dependent on: 1. Lysogenic prophage. 2. Low extracellular iron concentration.
  8. 8. Disease: Diphtheria  Upper respiratory tract infection.  Transmitted by droplets.  Characterized by: 1- Local pseudomembrane. 2- Toxemia.  Complications:  Airway obstruction  Toxic myocarditis and heart failure  Nerve paralysis
  9. 9. Clinical Manifestations - Cervical lymphadenitis (Bull neck) - Toxaemia with low grade fever D.D. of sore throat: 1- S. pyogenes 2- Vincent’s angina 3- C. diphtheriae
  10. 10. Diagnosis Mainly clinical Laboratory confirmation: A- Specimen: Throat swab from the pseudomembrane.
  11. 11. B- Direct Detection: Microscopic examination (Gram stain): • Gram-positive bacilli • Chinese letters appearance
  12. 12. B- Direct Detection: Microscopic examination (Methylene Blue stain): Meta-chromatic granules
  13. 13. 1- Loeffler’s serum: Best morphology 2- Blood tellurite agar: grey/black colonies 3- Blood agar to exclude S. pyogenes C- Cultivation:
  14. 14. D- Identification: Microscopic examination: 1- Gram stained smear: Gram-positive club-shaped bacilli (Chinese letters). 2- MB stained smear: showing meta-chromatic granules.
  15. 15. The isolated organism is Corynebacterium diphtheriae Is it Toxigenic or Not?
  16. 16. E- Toxigenicity Tests: a) Elek’s test: most common assay. b) PCR: detection of toxin gene. c) ELISA: detection of toxin from culture.
  17. 17. Elek’s test: An antigen-antibody reaction in which the Ag is soluble “Precipitation”.
  18. 18. Elek’s Test
  19. 19. Diagnosis of carriers Throat or nasal swabs are subjected to the same procedures: Isolation + Toxigenicity tests
  20. 20. What treatment is prescribed?  Treatment should be IMMEDIATELY started if diphtheria is clinically suspected.  Diphtheria antitoxin and antibiotics.  Treatment of symptoms & complications e.g. respiratory support.
  21. 21. How can we prevent this disease? By Vaccination Diphtheria toxoid + pertussis vaccine + tetanus toxoid in a trivalent vaccine: DPT For close contacts of a case: (booster of diphtheria toxoid + antibiotic chemoprophylaxis)
  22. 22. Diphtheroids Corynebacteria that resemble C.diphtheriae in morphology. They are mainly commensals.
  23. 23. Case  A 4-year-old male child presented with fever of 38°C.  Physical examination revealed clear chest, exudative pharyngitis and bilaterally enlarged cervical lymph nodes.  A throat culture was taken and a course of penicillin was started.
  24. 24. Case (cont.)  The child’s course worsened, he became increasingly lethargic, developed respiratory distress and was hospitalized.  On admission, he had a fever of 38°C and an exudate in the posterior pharynx described as a yellowish, thick membrane which bled when scraped and removed.  The patient’s medical history revealed that he had received no immunizations.
  25. 25. Listeria
  26. 26. Listeria monocytogenes Gram-positive rods (coccobacilli) Microscopic examination:
  27. 27. Listeria resembles Corynebacteria in morphology but is MOTILE.
  28. 28. Diseases  Abortion, premature delivery or sepsis during the peripartum period.  Neonatal meningitis  Septicaemia and meningitis (in immunocompromised adults).  Food poisoning (dairy products or undercooked meat)
  29. 29. Neonatal meningitis  Meningitis caused by Listeria is almost always seen in neonates.  Causes of Neonatal Meningitis: 1. Group B Streptococci 2. E. coli K1 3. Listeria monocytogenes
  30. 30. Case A one month old girl was admitted to hospital with acute meningitis. The Gram stain of CSF revealed Gram-positive short rods. What is the cause of neonatal meningitis? a. N. meningitidis, group A b. N. meningitidis, group C c. Listeria monocytogenes d. S. pneumoniae
  31. 31. How did the mother contract it?  Listeriosis is a food-borne infection.  Listeria resists drying, heating and freezing without forming spores.  Commonly contaminated food items: 1. Dairy products (esp. unpasteurized milk and soft cheeses). 2. Undercooked meat (chicken, hot-dogs). 3. Refrigerated food.
  32. 32. Review Questions
  33. 33. 1- C.diphtheriae is cultured on: a- Nutrient agar. b- Chocolate agar. c- Loffler’s serum. d- Lowenstein-Jensen medium. e- MacConkey’s agar.
  34. 34. 2- Blood tellurite agar is a(n): a- Enriched medium b- Enrichment medium c- Simple medium d- Selective and differential medium e- Indicator medium only
  35. 35. 3- Which of the following is a toxigenicity test for C.diphtheriae ? a- Elek’s test b- Coagulase c- Catalase test d- Culture on blood tellurite e- ELISA test for antibody detection
  36. 36. 4- C. diphtheriae has the following morphology: a- Gram negative cocci arranged in pairs b- Gram positive cocci arranged in chains c- Gram positive club-shaped bacilli d- Gram positive cocci in clusters e- Gram positive capsulated diplococci
  37. 37. 5- The toxin of C. diphtheriae is only produced by those strains that are: a- Encapsulated. b- Glucose fermenters. c- Sucrose fermenters. d- Lysogenic e- Endotoxin producers.
  38. 38. 6- A 1-week old newborn develops meningitis. Short gram-positive rods are isolated. The mother had eaten unpasteurized cheese during pregnancy. What is the most likely etiological diagnosis? a- C. diphtheriae. b- S. pyogenes. c- L. monocytogenes. d- S. pneumoniae. e- S. agalactiae
  39. 39. THANK YOU