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Streptococci (Gram positive cocci) Lecture 45

Streptococci (Gram positive cocci) Lecture 45. Faculty: Dr. Alvin Fox. Lancefield groups Hemolysis (alpha, beta, gamma) Group A streptococcus (S. pyogenes ) - Bacitracin susceptibility test - M, T, R proteins - Streptolysins O and S - F protein/lipoteichoic acid

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Streptococci (Gram positive cocci) Lecture 45

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  1. Streptococci (Gram positive cocci)Lecture 45 Faculty: Dr. Alvin Fox

  2. Lancefield groups Hemolysis (alpha, beta, gamma) Group A streptococcus (S. pyogenes) - Bacitracin susceptibility test - M, T, R proteins - Streptolysins O and S - F protein/lipoteichoic acid - Rheumatic fever/carditis/arthritis - Glomerulonephritis - Scarlet fever - Toxic shock-like syndrome - Bacteremia - Flesh-eating bacteria - Pyrogenic toxin - Erythrogenic toxin Group B streptococcus (S.agalactiae) - Neonatal septicemia/meningitis - CAMP test - Hippurate hydrolysis test Group D streptococcus - Urinary tract infection - Endocarditis - Bile-esculin test - Enterococci - Non-enterococci Large colony Minute colony Viridans streptococci Dental caries/endocarditis Key Words

  3. Streptococci • facultative anaerobe • Gram-positive • usually chains (sometimes pairs) • catalase negative • (staphylococci are catalase positive)

  4. Streptococcus in chains (Gram stain)

  5. Streptococcus pneumoniae (diplococcus). Fluorescent stain

  6. Identification : Lancefield groups • - carbohydrate antigens

  7. groupablestreptococci • A, B and D • frequent • C, G, F • less frequent

  8. Non-groupable • S. pneumoniae • pneumonia • viridans streptococci • e.g. S. mutans • dental caries

  9. hemolysis reaction - sheep blood agar • α (alpha) • partial hemolysis • green color • β (beta) • complete clearing • γ (gamma) - no lysis White colonies

  10. Hemolysis • Groups A an B • β • Group D • α or γ • S. pneumoniae and viridans • α

  11. Identification: hemolysis reaction +one biochemical characteristic

  12. Group A streptococcus (S. pyogenes)

  13. Group A streptococcal infections affect all ages peak incidence at 5-15 years of age

  14. S. pyogenes -suppurative • non-invasive • pharyngitis • skin infection, impetigo • invasive bacteremia • toxic shock-like syndrome • "flesh eating" bacteria • pyrogenic toxin

  15. Pyrogenic toxin • Superantigen • Non-specific activation of T cells • Cross-link antigen presenting cells (MHC) and T cell receptor • Cytokine production

  16. Scarlet fever • rash • “erythrogenic toxin”

  17. non-suppurative • rheumatic fever • inflammatory disease • life threatening • chronic sequalae • fever • heart • joints • rheumatic NOT rheumatoid arthritis

  18. Rheumatic fever -etiology • M protein • cross-reacts heart myosin • autoimmunity • Cell wall antigens • poorly digested in vivo • persist indefinitely

  19. Rheumatic fever • penicillin • terminates pharyngitis • decreases carditis

  20. Acute glomerulonephritis • immune complex disease of kidney

  21. Major pathogenesis factors • lipoteichoic acid/F protein • fimbriae • binds to epithelial cells • M protein • anti-phagocytic

  22. S. pyogenes lipoteichoic acid F-protein fibronectin epithelial cells

  23. r r r r r r M protein IMMUNE Complement IgG M protein NON-IMMUNE peptidoglycan fibrinogen

  24. M protein • major target • natural immunity • strain variation • antigenicity • re-infection • occurs with different strain

  25. Capsules • Anti-phagocytic • mucoid strains

  26. Isolation and identification • βhemolytic colonies • bacitracin inhibits growth • β hemolytic colonies • group A antigen

  27. βhemolysis • hemolysin O • sensitive oxygen • hemolysin S • insensitive oxygen

  28. Modern Rapid “Strep” Test Throat swab extract (+/- streptococcal antigen) - + Antibody Liposome Streptococcal antigen

  29. Post-infectious diagnosis (serology) • antibodies to streptolysin O • important if delayed clinical sequelae occur

  30. Typing Traditional serotyping of proteins: - M - T - R Current: - Sequencing of M protein gene

  31. Group B streptococcus • neonatal meningitis • septicemia • transmission • vaginal flora

  32. Group B streptococcus - identification • β hemolysis • hippurate hydrolysis • CAMP reaction • increases β hemolysis of S. aureus

  33. Group D streptococcus • Growth on bile esculin agar • black precipitate • 6.5% saline • grow • enterococci • no growth • non-enterococci

  34. Enterococci • distantly related to other streptococci • genus Enterococcus • gut flora • urinary tract infection • fecal contamination • opportunistic infections • particularly endocarditis • most common E. (S.) faecalis

  35. Enterococci • resistant to many antibiotics • including vancomycin • terminal D-ala replaced by D-lactate

  36. Minute colony streptococci • Various groups/hemolysis (e.g. group A) • genetically distinct • from large colony (e.g. S. pyogenes) • no rheumatic fever Large colony Minute colony

  37. Viridans streptococci • diverse species • oral • dental caries • α hemolytic and negative for other tests • non-groupable. • includes S. mutans • occassionalendocarditis after tooth extraction

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