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
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
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
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
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?
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?
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
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
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?