Diphtheria - Prac. Microbiology

  • Published on

  • View

  • Download




  • 1. Gram positive bacilli Non-spore forming - Corynebacterium - Listeria Spore- forming - Bacillus - Clostridium
  • 2. Non-spore forming Corynebacterium
  • 3. Corynebacterium Some species are part of normal flora of skin and mm. Medically important species is Corynebacterium diphtheriae
  • 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. Methylene blue stain: Beaded appearance
  • 6. Culture Characters Aerobic. Growth on: 1. Blood agar 2. Loefflers serum: Best morphology 3. Blood tellurite agar: Selective & differential Grey to black colonies
  • 7. Virulence factors Diphtheria ExotoxinDiphtheria Exotoxin Exotoxin is dependent on: 1. Lysogenic prophage. 2. Low extracellular iron concentration.
  • 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. Clinical Manifestations - Cervical lymphadenitis (Bull neck) - Toxaemia with low grade fever D.D. of sore throat: 1- S. pyogenes 2- Vincents angina 3- C. diphtheriae
  • 10. Diagnosis Mainly clinical Laboratory confirmation: A- Specimen: Throat swab from the pseudomembrane.
  • 11. B- Direct Detection: Microscopic examination (Gram stain): Gram-positive bacilli Chinese letters appearance
  • 12. B- Direct Detection: Microscopic examination (Methylene Blue stain): Meta-chromatic granules
  • 13. 1- Loefflers serum: Best morphology 2- Blood tellurite agar: grey/black colonies 3- Blood agar to exclude S. pyogenes C- Cultivation:
  • 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. The isolated organism is Corynebacterium diphtheriae Is it Toxigenic or Not?
  • 16. E- Toxigenicity Tests: a) Eleks test: most common assay. b) PCR: detection of toxin gene. c) ELISA: detection of toxin from culture.
  • 17. Eleks test: An antigen-antibody reaction in which the Ag is soluble Precipitation.
  • 18. Eleks Test
  • 19. Diagnosis of carriers Throat or nasal swabs are subjected to the same procedures: Isolation + Toxigenicity tests
  • 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. 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. Diphtheroids Corynebacteria that resemble C.diphtheriae in morphology. They are mainly commensals.
  • 23. Case A 4-year-old male child presented with fever of 38C. 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. Case (cont.) The childs course worsened, he became increasingly lethargic, developed respiratory distress and was hospitalized. On admission, he had a fever of 38C and an exudate in the posterior pharynx described as a yellowish, thick membrane which bled when scraped and removed. The patients medical history revealed that he had received no immunizations.
  • 25. Listeria
  • 26. Listeria monocytogenes Gram-positive rods (coccobacilli) Microscopic examination:
  • 27. Listeria resembles Corynebacteria in morphology but is MOTILE.
  • 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. 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. 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. 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. Review Questions
  • 33. 1- C.diphtheriae is cultured on: a- Nutrient agar. b- Chocolate agar. c- Lofflers serum. d- Lowenstein-Jensen medium. e- MacConkeys agar.
  • 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. 3- Which of the following is a toxigenicity test for C.diphtheriae ? a- Eleks test b- Coagulase c- Catalase test d- Culture on blood tellurite e- ELISA test for antibody detection
  • 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. 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. 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. THANK YOU