Streptococcus pyogenes is a Gram positive coccus that forms chains and causes beta hemolysis on blood agar. It is classified by Lancefield grouping based on cell wall carbohydrates and Griffith typing based on M proteins. S. pyogenes causes respiratory, skin, and genital infections and can lead to post-streptococcal sequelae like rheumatic fever and glomerulonephritis. Penicillin is usually the treatment of choice.

1. STREPTOCOCCUS
Dr.M.Malathi
Postgraduate final year
Department of Microbiology
Chengalpattu Medical College

2. Introduction
• Gram positive cocci
• Arrangement : chains or pairs
• Part of normal flora
• Causes pathogenic infections also

3. Classification of Streptococci
• Brown`s classification
• Lancefield grouping
• Griffith typing

4. Brown`s classification

5. Hemolysis

6. Lancefield grouping

7. Group A betahemolytic Streptococci
Streptococcus pyogenes
Morphology:
• Spherical to oval cocci
• Arranged in chains, more in liquid medium
• Why chain formation?
• Longest chain is produced by Streptococcus
salivarius (Commensal)
• Non motile
• Non sporing

8. Gram positive cocci in chains

9. Cultural characteristics
• Aerobe and facultative anaerobe
• Temperature – 37 deg C
• Needs enrichment with blood or serum
• Blood agar – small colonies with beta type of
hemolysis around them
• Liquid media – granular turbidity

10. Biochemical reactions
• Ferments sugars – acid , no gas
• Catalase negative
• PYR test (Pyrolidonyl beta naphthylamide)
positive
• Ribose – not fermented
• Not bile soluble

11. Antigenic structure
• Structural antigens – Cell wall antigens
• Toxins
• Enzymes

12. Structural antigens
• Capsule – not antigenic
• Cell wall – Group specific carbohydrate
Extraction methods:
1. Lancefield`s acid extraction method
2. Fuller`s method
3. Maxted`s method
4. Rantz and Randall`s method

13. • Protein antigens
1. M protein : most virulent; heat and acid
stable, but susceptible to tryptic digestion. 80
types identified. Griffith typing.
2. T protein : acid labile, trypsin resistant. Not
virulent.
3. R protein: not virulent
• Fimbrial antigens: for attachment in
epithelial cells

14. Antigenic cross - reactions
Streptococcus pyogenes Human
Capsular hyaluronic acid Human synovial fluid
Cell wall proteins Myocardium
Group A carbohydrates Cardiac valves
Cytoplasmic membrane
antigens
Vascular intima
Peptidoglycan Skin antigens

15. Toxins and enzymes
• Streptolysin – O, S
• Pyrogenic exotoxin
• Streptokinase
• Deoxyribonucleases (Streptodornase)
• NADase
• Hyaluronidase
• Serum opacity factor

16. Pathogenicity
• Suppurative diseases:
1. Respiratory infections
2. Skin and soft tissue infections
3. Genital infections
• Non suppurative sequelae:
1. Acute rheumatic fever
2. Acute glomerulonephritis

17. Respiratory infections
• Primary site – throat
• Adherence – by pili
• Tonsillitis
• Pharyngitis
• Otitis media
• Streptococcal pneumonia
• Throat infection – sequelae – Acute rheumatic
fever

18. Skin and soft tissue infections
• Cellulitis
• Septicemia
• Erysipelas – diffuse infection – superficial
lymphatics – older patients
• Impetigo – skin lesions – children – leads to
sequelae – Acute glomerulonephritis

19. Cellulitis

20. Necrotising faciitis :
• M types 1 and 3 forming pyrogenic exotoxin A
• High fatality
• Flesh eating bacteria
• Shock, DIC
• Treatment with penicillin – not effective
• Vancomycin – DOC in life threatening
infections

21. Effect of flesh eating bacteria 

22. Genital infections
• Normal inhabitants of the female genitalia
• Puerperal sepsis

23. Acute rheumatic fever
• Site of infection – Throat
• Prior sensitization is essential
• Serotype – Any
• Marked immune response
• Unaffected complement level
• Genetic susceptibility – present
• Repeated attacks – common
• Penicillin prophylaxis is essential

24. Acute glomerulonephritis
• Site of infection – Throat or skin
• Prior sensitisation – not necessary
• Serotype – 49,53-55,59-61 and 1,12
• Moderate immune response
• Complement level - lowered
• Genetic susceptibility – Absent
• Repeated attacks – Absent
• Penicillin prophylaxis is not indicated

25. Case history
• 7 year old girl
• Fever with severe sore throat
• Bilateral enlarged tonsils and exudates
What investigation?
What culture plate you will use?

26. • Throat swab
• Direct Gram stain – GPC in chains
• Culture – Transport medium (Pike`s medium)
• Culture – sheep blood agar
• Rapid diagnostic kits with specific antisera
• Bacitracin sensitivity
• ASO titre
• Anti DNAase B

27. Case history
• Nine year old girl
• Fever and sore throat
• On throat culture – Group A Streptococci
• O/E, pain and tender swelling, palpable
effusion of the right knee, culture of aspirate
is negative.
• CXR – mild congestive heart failure
• Murmur heard at cardiac apex
• Diagnosis ?
• What investigation?

28. Check ASO titre

29. Case history
• Seven year old boy
• Skin infection
• Five days later, coloured urine and pitting
oedema
• Elevated BP, 4+ proteinuria, elevated serum
creatinine
• Diagnosis?
• What investigation?

30. Prophylaxis
• Penicillin prophylaxis fro the prevention of
rheumatic fever
• Not needed for AGN

31. Treatment
• All are sensitive to Penicillin G
• If patient is having anaphylaxis for penicillin G
 Give erythromycin
• Some strains are resistant to erythromycin

32. Group B beta hemolytic Streptococci
Streptococcus agalactiae
• Neonatal infection
• Most common cause of neonatal meningitis
• Source – from the maternal vagina during
birth
• GBS – puerperal sepsis, pneumonia
• Diagnostic markers – Hippurate hydrolysis,
CAMP test

33. CAMP test
• Christie, Atkins and Munch-Peterson
• When S.agalactiae is inoculated perpendicular
to a streak of S.aureus grown on blood agar 
an accentuated zone of hemolysis occurs

34. CAMP TEST

35. Group C beta hemolytic Streptococci
Streptococci equisimilis
• Upper respiratory infections
• Endocarditis, osteomyelitis, brain abscess
• Penicillin tolerance
• Treat with penicillin and gentamicin
• Source of streptokinase used for thrombolytic
therapy in patients

36. Group F beta hemolytic Streptococci
Streptococcus MG
• Grow poorly on blood agar
• Minute streptococci
• Streptococcus MG – alphalytic strain –
isolated from Primary atypical pneumonia

37. Enterococcus
• E.faecalis
• E.faecium
• E.durans

38. Special features
• Grow in the presence of 40% bile
• 6.5% sodium chloride
• pH 9.6
• Growth at 45degC
• Tiny magenta coloured colonies in Mac Conkey
agar
• Heat resistant – survives 60degC for 30 minutes
• Pairs of oval cocci, arranged at an angle to each
other
• Non hemolytic

39. • Identification – mannitol, sucrose, sorbitol
fermentation , bile Esculin hydrolysis
• Present in intestine, genital tract and saliva
• Urinary tract infection and wound infection.
• Intrinsically resistant to cephalosporins
• Treatment:
Penicillin + Aminoglycosides
Vancomycin

40. Viridans group
• Streptococci normally resident in the mouth and
upper respiratory tract
• Alpha lysis on blood agar
• Cannot be categorised under lancefield antigenic
groups
• Types:
1. S.mitis
2. S.mutans
3. S.salivarius
4. S.sanguis

41. • Causes dental caries
• Tooth extraction – seeding into blood stream -
endocarditis – hence give prophylactic
antibiotics

42. Summary
• Types of hemolysis?
• What is the basis for lancefield grouping?
• What is the basis for Griffith typing?
• Name one example for alpha hemolysis?
• Name one example for beta hemolysis?
• Name one example for gamma hemolysis?
• Significant titre for ASO?
• What are the post streptococcal sequelae?