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Streptococcus
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- 2. Streptococci Characters of Streptococci Grampositive cocci Size 1µm Chains or pairs Non motile Non spore forming Facultative anaerobes Fastidious Catalase negative
- 3. Classification of Streptococci Accordingto: – 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 BloodAgar Hemolysis on BA – -hemolysis Partial hemolysis Small zone Viridans streptococci Green discoloration around colonies e.g. S. pneumoniae & S. viridans – -hemolysis Complete hemolysis Clear zone of hemolysis around colonies 2-4mm zone Hemolytic streptococci e.g. Lancefield Group A & B (S. pyogenes & S. agalactiae) – -hemolysis No hemolysis e.g. Group D (Enterococcus sp.)
- 5. Hemolysis on Bloodagar -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 Streptococci Group A S. pyogenes Group B S. agalactiae Group C S. equisimitis Group D Enterococcus Lanciefield classification Other groups (E-U)
- 7. A and O Fibrinlysis Dnase RNase A,B,C Super antigen TSS and scarlet fever Antigens
- 8. Disease caused byS. pyogenes (Group A) Suppurative Non-Invasive Pharyngitis (Sore throat) - inflammation of the pharynx, tonsillitis, otitis media, mastoiditis, rarely meningitis Pyoderma- Impetigo- localised pus-producing lesions usually occur on face, arms, or legs -
- 9. Suppurative Invasive Erysipelas- diffuse infectionof skin, involves superficial lymphatics. well demarcated borders Cellulitis- infection of skin & subcutaneous tissue, spreading 3. Necrotizing Fasciitis (Streptococcal Gangrene)— This is infection of the subcutaneous tissues and fascia.There is extensive and very rapidly spreading necrosis ofthe skin and subcutaneous tissues Puerperal Fever—If the streptococci enter the uterus after delivery, puerperal fever develops, which is essentially a septicemia originating in the infected wound (endometritis) Bacteremia/Sepsis—Infection of traumatic or surgical wounds with streptococci results in bacteremia
- 10. Toxin Mediated Diseases Scarletfever- 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 shock, bacteremia, respiratory failure, and multiorgan failure
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- 12. Non Suppurative complicationsor sequelae – Rheumatic fever: following pharyngitis carditis, poly arthritis, damage to heart valves fever, malaise, a migratory nonsuppurative polyarthritis, and evidence of inflammation of all parts of the heart (endocardium, myocardium, pericardium) 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
- 13. Pathogenesis & VirulenceFactors 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
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- 16. Diagnosis – Acute infection –culture – Nonsuppurative complication – antibody – diagnosis – Presumptive – gram staining (Pus/CSF) – Sheep blood agar culture – hemolysis (-ve to H.hemolyticus) – Rheumatic fever, glomerulonephritis – Ab to toxin – Streptozyme test – passive hemagglutination test
- 17. Prophylaxis Prevention of rheumaticfever Long term administration of penicillin Prevents heart damage Not applicable for glomerulonephritis
- 18. Treatment Beta hemolytic groupA- Penicillin G Erythromycin and cephalexin – for allergic
- 19. Summary Streptococcus general characters LancefieldClassification Toxins / Enzymes of S. pyogenes Infections / Sequelae caused Laboratory Diagnosis