1. Streptococci

2. Gram-positive cocci in chains
• Gram positive cocci arranged in chains

3. Planes of division

4. Catalase Test
Catalase +ve
Catalase –ve
Staphylococci
Streptococci

5. • Growth requires enriched media containing
blood or serum.

6. Haemolysis on sheep blood agar can be used for
distinguishing between streptococci

7. Group Antigens
• Cell wall Carbohydrate antigens
• Lancefield group antigens
A – W (except I & J)

8. Streptococcus pyogenes
Group A Streptococci
Gram-positive cocci in chains
Beta hemolytic

9. Virulence Factors

11. Pharyngitis
• Sore Throat
• Tonsillitis

12. Scarlet Fever

13. Skin & Soft Tissue Infections
• Impetigo
– Lesions on
extremities
– Commonly on face
– Pustular and crusty

14. Skin & Soft Tissue Infections
Cellulitis & Erysipelas

15. Invasive streptococcal infections
•
•
•
•
Puerperal fever
Acute endocarditis
Necrotizing fasciitis
Toxic shock syndrome

16. Necrotizing Fasciitis

17. Laboratory Diagnosis
• Specimen:
– Throat swab
– Pus
– CSF
– Blood

18. • Direct detection
– Gram-stained smear
S. pyogenes
– Detection of group A streptococcal antigen
from throat swab.

20. • Culture:
Blood
Throat swab
Pus
CSF
Culture
on
Blood
culture
bottle
Culture on
Blood Agar
subculture

21. • Identification :
A. Colony morphology

22. B. Gram-stained smear

23. C. Catalase test
negative

24. D. Bacitracin sensitivity test

25. E. Agglutination by group A antibody .

26. Viridans streptococci

27. Diseases:
- Subacute Bacterial
Endocarditis (SBE)
- Dental Caries

28. Laboratory diagnosis of SBE
Blood culture technique

29. Streptococcus pneumoniae
Gram positive
capsulated diplococci.
Alpha haemolytic .

30. Quellung test :

31. Pneumococcal diseases
Three major diseases:
• Pneumonia
• Meningitis
• Otitis media

32. Laboratory diagnosis
A-Specimens:
– Sputum
– CSF
– Ear discharge
– Blood

33. B- Direct detection :
1- Gram-stained smear
2- Quellung test
3- Detection of capsular polysaccharide antigen
in CSF by slide agglutination test

34. • Culture:
Blood
Throat swab
Pus
CSF
Culture
on
Blood
culture
bottle
Culture on
Blood Agar
subculture

35. Identification :
1-Colony morphology
2-Gram-stained smear
3-Differentiation from viridans streptococci

36. A. Growth inhibition by optochin

37. B. Solubility of colonies in bile

38. C. Capsular polysaccharide antigen detection

39. D. Quellung reaction

40. E. DNA probe specific to S. pneumoniae

41. F. Virulence to mice

42. Populations at risk of being infected with
S. pneumoniae
• Asplenic individuals
• infants
• Immunosuppressed individuals
• Alcoholics

43. 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

44. Enterococcus
•
•
Gram +ve cocci
singly / in pairs /short chains

45. Enterococcus
•
•
•
Catalase negative
Hydrolyze esculin in presence
of bile salts
Lancefield group D

46. Enterococcus Infections
•
•
•
•
•
UTI
Intra-abdominal & pelvic wound infections
Bacteraemia
Endocarditis
Abscesses, meningitis, peritonitis, osteomyelitis &
wound infection

47. 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.

48. 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?

49. A. Specimen
Specimen
Throat swabs

50. Direct detection:
- Gram-stained smear
Gram-positive cocci
arranged in chains
amongst pus cells

51. B. Direct detection
- Detection of group A streptococcal
antigen from throat swab.

52. Culture:
On blood agar: β- hemolysis

53. Identification from colonies:
1.Gram-stained smear
Gram positive cocci
in chains
2. Catalase test
catalase negative

54. 3.Bacitracin sensitivity test
Bacitracin sensitive
Group A
(S. pyogenes)

55. What treatment would you offer her?
• Penicillin, or erythromycin if allergic to
penicillin.

56. 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

57. Rheumatic Fever
Immune response against Strept. antigens
similar to heart antigens.

58. Post-streptococcal glomerulonephritis
Deposition of Ag-Ab complexes, activation
of complement.

59. 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 .

60. 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

61. Review Questions

62. 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

63. 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

64. 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

65. 4. Streptococcus pyogenes can not be isolated
in case of:
a) Pharyngitis.
b) Puerperal fever.
c) Acute endocarditis.
d) Rheumatic fever.
e) Necrotizing fasciitis.

66. 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

67. 6. Blood culture is required for the diagnosis of:
a) Subacute bacterial endocarditis
b) Pharyngitis
c) Glomerulonephritis
d) Rheumatic fever
e) Scarlet fever

68. THANK YOU