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Streptococcus

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Streptococcus Prof. Jyotsna Agarwal Dept Microbiology KGMU Streptococci Characters of Streptococci Gram positive cocci Size 1 m Chains or pairs Non motile Non spore ... – PowerPoint PPT presentation

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Title: Streptococcus


1
Streptococcus
  • Prof. Jyotsna Agarwal
  • Dept Microbiology
  • KGMU

2
Streptococci
  • Characters of Streptococci
  • Gram positive cocci
  • Size 1µm
  • Chains or pairs
  • Non motile
  • Non spore forming
  • Facultative anaerobes
  • Fastidious
  • Catalase negative

3
Classification of Streptococci
  • According to
  • Oxygen requirement
  • Anaerobic (Peptostreptococcus)
  • Aerobic or facultative anaerobic (Streptococcus)
  • Hemolysis on Blood Agar- a, ß, ?
  • Lancefield classification- for ß hemolytic
    streptococci, based on C antigen

4
Hemolysis on Blood Agar
  • Hemolysis on BA
  • ?-hemolysis
  • Partial hemolysis
  • Green discoloration around colonies
  • e.g. S. pneumoniae S. viridans
  • ?-hemolysis
  • Complete hemolysis
  • Clear zone of hemolysis around colonies
  • e.g. Lancefield Group A B (S. pyogenes S.
    agalactiae)
  • ?-hemolysis
  • No hemolysis
  • e.g. Group D (Enterococcus sp.)

5
Hemolysis on Blood agar
?-hemolysis
?-hemolysis
?-hemolysis
6
Lancefield Classification- ß hemolytic
  • Classification based on C- carbohydrate antigen
    of cell wall
  • 20 Lancefield groups from A-H K-V
  • One or more species per group
  • Group A- Further subdivided based on M, T, R
    protein (Griffith typing) in to 80 sertypes

7
Disease caused by S. pyogenes (Group A)
  • Suppurative
  • Non-Invasive
  • Pharyngitis - inflammation of the pharynx,
    tonsillitis, otitis media, mastoiditis, rarely
    meningitis
  • Pyoderma- Impetigo- localised pus-producing
    lesions usually occur on face, arms, or legs

8
  • Suppurative
  • Invasive
  • Erysipelas- diffuse infection of skin, involves
    superficial lymphatics. well demarcated borders
  • Cellulitis- infection of skin subcutaneous
    tissue, spreading

9
Toxin Mediated Diseases
  • Scarlet fever- rash begins on chest spreads
    across body
  • Necrotizing fasciitis-Pyrogenic exotoxin produced
    by some trains of S. pyogenes- Can lead to DIC.
  • Streptococcal Toxic Shock Syndrome

10
  • Non Suppurative complications or sequelae
  • Rheumatic fever following pharyngitis
  • carditis, poly arthritis, damage to heart valves
  • potentially fatal
  • Acute Glomerulonephritits- following skin
    infection
  • Immune complex mediated disease
  • inflammation of glomeruli due to Ag-Ab complex
    deposit on basement membrane
  • Clinically- Hematuria, Proteinuria, Hypertension
  • Good prognosis

11
Pathogenesis Virulence Factors
  • Structural components
  • M protein inhibits phagocytosis of bacteria
  • Lipo teichoic acid helps in adhesion of bactera
  • Capsule- camouflages bacteria
  • Enzymes
  • Streptokinases- fibrinolysin
  • Deoxyribonucleases
  • Hyaluronidase
  • Pyrogenic / Erythrogenic exotoxin
  • Hemolysins
  • Streptolysin O- Oxygen labile, antigenic
  • Streptolysin S- serum soluble

Facilitate spread of streptococci in tissues
12
Lab Diagnosis
  • Sample -Throat swab, pus / swab
  • Gram Stain- GPC in chains
  • Culture on Blood agar- beta hemolytic colonies,
    catalase negative

13
Bacitracin sensitivity
  • Principle
  • for presumptive identification of group A
  • distinguish between S. pyogenes from other beta
    hemolytic streptococci
  • Strep. Pyogenes sensitive to Bacitracin giving
    zone of inhibition around disk

14
Differentiation of ?-hemolytic streptococci
  • Lanciefield Classification
  • Bacitracin susceptibility Test
  • Specific for S. pyogenes (Group A)
  • CAMP test
  • Specific for S. agalactiae (Group B)- normal
    flora of genital tract in women, can cause
    neonatal meningitis

15
CAMP test
  • Principle
  • Group B streptococci produce extracellular
    protein (CAMP factor)
  • CAMP act synergistically with staphylococcal
    ?-lysin to increase lysis of RBCs

16
Summary
  • Streptococcus general characters
  • Lancefield Classification
  • Toxins / Enzymes of S. pyogenes
  • Infections / Sequelae caused
  • Laboratory Diagnosis
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