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Streptococcus

Streptococcus. Prof. Jyotsna Agarwal Dept Microbiology KGMU. Characters of Streptococci Gram positive cocci Size 1 µ m Chains or pairs Non motile Non spore forming Facultative anaerobes Fastidious Catalase negative. Streptococci. Classification of Streptococci. According to:

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Streptococcus

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  1. Streptococcus Prof. JyotsnaAgarwal Dept Microbiology KGMU

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

  3. Classification of Streptococci • According to: • Oxygen requirement • Anaerobic (Peptostreptococcus) • Aerobic or facultative anaerobic (Streptococcus) • Hemolysis on Blood Agar- α, β, Ƴ • Lancefield classification- for β 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- βhemolytic • 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-Pyrogenicexotoxin 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 • Lipoteichoic acid helps in adhesion of bactera • Capsule- camouflages bacteria • Enzymes • Streptokinases- fibrinolysin • Deoxyribonucleases • Hyaluronidase • Pyrogenic / Erythrogenicexotoxin • 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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