Sreptococci - Prac. Microbiology

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Sreptococci - Prac. Microbiology

  1. 1. Streptococci
  2. 2. Gram-positive cocci in chains • Gram positive cocci arranged in chains
  3. 3. Planes of division
  4. 4. Catalase Test Catalase +ve Catalase –ve Staphylococci Streptococci
  5. 5. • Growth requires enriched media containing blood or serum.
  6. 6. Haemolysis on sheep blood agar can be used for distinguishing between streptococci
  7. 7. Group Antigens • Cell wall Carbohydrate antigens • Lancefield group antigens A – W (except I & J)
  8. 8. Streptococcus pyogenes Group A Streptococci Gram-positive cocci in chains Beta hemolytic
  9. 9. Virulence Factors
  10. 10. Pharyngitis • Sore Throat • Tonsillitis
  11. 11. Scarlet Fever
  12. 12. Skin & Soft Tissue Infections • Impetigo – Lesions on extremities – Commonly on face – Pustular and crusty
  13. 13. Skin & Soft Tissue Infections Cellulitis & Erysipelas
  14. 14. Invasive streptococcal infections • • • • Puerperal fever Acute endocarditis Necrotizing fasciitis Toxic shock syndrome
  15. 15. Necrotizing Fasciitis
  16. 16. Laboratory Diagnosis • Specimen: – Throat swab – Pus – CSF – Blood
  17. 17. • Direct detection – Gram-stained smear S. pyogenes – Detection of group A streptococcal antigen from throat swab.
  18. 18. • Culture: Blood Throat swab Pus CSF Culture on Blood culture bottle Culture on Blood Agar subculture
  19. 19. • Identification : A. Colony morphology
  20. 20. B. Gram-stained smear
  21. 21. C. Catalase test negative
  22. 22. D. Bacitracin sensitivity test
  23. 23. E. Agglutination by group A antibody .
  24. 24. Viridans streptococci
  25. 25. Diseases: - Subacute Bacterial Endocarditis (SBE) - Dental Caries
  26. 26. Laboratory diagnosis of SBE Blood culture technique
  27. 27. Streptococcus pneumoniae Gram positive capsulated diplococci. Alpha haemolytic .
  28. 28. Quellung test :
  29. 29. Pneumococcal diseases Three major diseases: • Pneumonia • Meningitis • Otitis media
  30. 30. Laboratory diagnosis A-Specimens: – Sputum – CSF – Ear discharge – Blood
  31. 31. B- Direct detection : 1- Gram-stained smear 2- Quellung test 3- Detection of capsular polysaccharide antigen in CSF by slide agglutination test
  32. 32. • Culture: Blood Throat swab Pus CSF Culture on Blood culture bottle Culture on Blood Agar subculture
  33. 33. Identification : 1-Colony morphology 2-Gram-stained smear 3-Differentiation from viridans streptococci
  34. 34. A. Growth inhibition by optochin
  35. 35. B. Solubility of colonies in bile
  36. 36. C. Capsular polysaccharide antigen detection
  37. 37. D. Quellung reaction
  38. 38. E. DNA probe specific to S. pneumoniae
  39. 39. F. Virulence to mice
  40. 40. Populations at risk of being infected with S. pneumoniae • Asplenic individuals • infants • Immunosuppressed individuals • Alcoholics
  41. 41. So, how to protect them? • A vaccine is available. – Capsular polysaccharide vaccine – Antigens from 23 serotypes. • Under age of TWO years: – Pneumococcal conjugate vaccine – Capsular polysaccharide + protein carrier
  42. 42. Enterococcus • • Gram +ve cocci singly / in pairs /short chains
  43. 43. Enterococcus • • • Catalase negative Hydrolyze esculin in presence of bile salts Lancefield group D
  44. 44. Enterococcus Infections • • • • • UTI Intra-abdominal & pelvic wound infections Bacteraemia Endocarditis Abscesses, meningitis, peritonitis, osteomyelitis & wound infection
  45. 45. Case 1 A 10-year-old girl presents to her primary care physician with : o severe sore throat, o fever, o headache, nausea, and abdominal pain.
  46. 46. Case (cont.) Examination shows: The back of her throat is covered with a purulent exudate with white pus-filled nodules. How can you reach a diagnosis?
  47. 47. A. Specimen Specimen Throat swabs
  48. 48. Direct detection: - Gram-stained smear Gram-positive cocci arranged in chains amongst pus cells
  49. 49. B. Direct detection - Detection of group A streptococcal antigen from throat swab.
  50. 50. Culture: On blood agar: β- hemolysis
  51. 51. Identification from colonies: 1.Gram-stained smear Gram positive cocci in chains 2. Catalase test catalase negative
  52. 52. 3.Bacitracin sensitivity test Bacitracin sensitive Group A (S. pyogenes)
  53. 53. What treatment would you offer her? • Penicillin, or erythromycin if allergic to penicillin.
  54. 54. This patient may present afterwards with one of Post - Streptococcal sequelae. What are they? And what is the underlying mechanism? 1. 2. Rheumatic Fever Post-Streptococcal glomerulonephritis
  55. 55. Rheumatic Fever Immune response against Strept. antigens similar to heart antigens.
  56. 56. Post-streptococcal glomerulonephritis Deposition of Ag-Ab complexes, activation of complement.
  57. 57. Diagnosis of ARF No single test is pathognomonic . Diagnosis is based on modified Jones criteria: a) Evidence of recent S .pyogenes infection b) Two of the five major criteria ,or one major and two minor criteria .
  58. 58. The evidence of recent streptococcal infection a-History of acute tonsillitis . b-Elevation of ASO titre above 200 units . N.B. In case of AGN: Anti-DNAse
  59. 59. Review Questions
  60. 60. 1. The simplest test to differentiate staphylococci from streptococci is the: a) Coagulase test b) Bacitracin test c) Gram stain d) Catalase test e) Optochin test
  61. 61. 2. Group A streptococcus growing on a blood agar plate, shows which of the following: a) Alpha hemolysis, a clear zone surrounding the colonies b) Alpha hemolysis, a green zone surrounding the colonies c) Beta-hemolysis, a clear zone surrounding the colonies d) Beta-hemolysis, a green zone surrounding the colonies e) No haemolysis
  62. 62. 3.Susceptibility to bacitracin is used to differentiate: a) Streptococcus pneumoniae from Staphylococcus aureus. b) Streptococcus pyogenes from Streptococcus pneumoniae. c) Streptococcus pneumoniae from viridans streptococci. d) Streptococcus pyogenes from non group A beta haemolytic streptococci. e) Streptococcus pyogenes from Staphylococc aureus
  63. 63. 4. Streptococcus pyogenes can not be isolated in case of: a) Pharyngitis. b) Puerperal fever. c) Acute endocarditis. d) Rheumatic fever. e) Necrotizing fasciitis.
  64. 64. 5. The inhibition of growth of alpha-hemolytic colonies by optochin indicates: a) Streptococcus pyogenes b) Viridans streptococci c) Streptococcus pneumoniae d) Staphylococcus aureus e) Enterococci
  65. 65. 6. Blood culture is required for the diagnosis of: a) Subacute bacterial endocarditis b) Pharyngitis c) Glomerulonephritis d) Rheumatic fever e) Scarlet fever
  66. 66. THANK YOU

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