MMI 301-Exam 2-Lecture 12: Streptococci

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MMI 301-Exam 2-Lecture 12: Streptococci
2013-10-25 18:54:28

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  1. Significant Streptococcal species
    Pyogenes, agalactiae, and pneumoniae
  2. Doctor who instituted hand cleaning between patients, fought Pyogenes
  3. Historical Classification, Hemolysis Classifications
    • -Separated based on hemolytic activity on blood auger plates
    •      -alpha, beta, or gamma hemolytics       -Alpha:green coloration of surroundings
    • -Beta:Complete lysis, clear surrounding -Gamma:No change
  4. Streptococcal Serology
    • Discovered by Lancefield
    • -Discovered that streptococci possessed unique cell wall carbohydrates
    • -Allowed more specific serotyping
    • -Pyogenes: Group A strep
    • -Agalactiae:Group B
    • -Pneumoniae: Originally classified as
    • Diplococcus, after DNA sequencing went to Streptococcus
  5. Other Strains of Strep
    • -Viridans group: represent oral commensal species
    •     -Cause endocarditis when it gets into blood
    •     -Will attack congenitally abnormal/damaged scarred heart valves
    •            -Stick to valve and multiply
  6. Group A Strep (S. pyogenes)
    • -Capsule, M Protein, lipoteichoic acid, streptolysin O, C5a peptidase, tissue destroying
    • enzymes
  7. Group A Strep (S. pyogenes) M protein
    • -250 different M-protein types
    • -Show differences in repeat regions and binding of host molecules
    • -Binds and inhibits IgA/C4BP to stop classical pathway/IgAmediated phagocytosis
  8. Strep. pyogenes: C5a peptidase/SpeB
    -Destroy C5a/CXC chemokines that serve as signaling molecules
  9. Strep. pyogenes: Cytolytic toxins:
    • -Streptolysin S: is a 2.7 kD modified peptide
    • -Streptolysin O: is a pore-forming toxin (cholesterol-dependent cytolysin)
  10. Strep. pyogenes enzymes: SpeA,
    SpeC, SpeG-M, SmeZ, SSA
    • -Superantigens
    • -Cause release of IL-1, IL-2, IL-6, TNF-alpha, gamma-IFN
  11. Strep pyogenes Epidemiology
    -Group A carried in throat of 15-20% of all children and adults w/o evidence of disease
  12. Strep. pyogenes causes:
    • -Suppurative streptococcal diseases:                                                         
    • -Pharyngitis:Strep_throat                                                           -Scarlet fever: results from erythrogenic toxin
    • -Streptococcal Toxic Shock: fever
    • rash, vomiting, diarrhea, desquamation, renal failure, confusion. Caused by
    • superantigen                                                

    • -Impetigo: pustules around nose and mouth     
    • -Necrotizing fasciitis: Flesh-eating
    • disease. Starts from trauma, excessive pain at site, progresses to blisters on
    • skin/necrosis
  13. Rheumatic Fever
    • -Inflammatory disease of connective tissue, usually manifested on heart valves
    • -Anti-body response to Group A strep antigens leads to cross-reactive antibodies
    •      -attach to connective tissue, leads local complement activation
    •      -destroys tissuse
    •      -seen mostly in 5-15
  14. B. acute Glomerulonephritis (AGN)
    • -Kidneys have filters (glomeruli)
    •      -Attach to small fluid collecting tubes
    •      -Filter blood
    •      -Waste to bladder
    • -Inflammation of glomeruli
    •       -leads to loss of filtration
    •       -Accumulation of waste, kidney failure
    • -Skin or throat Group A is followed by AGN
    •       -Caused by accumulation of Abs-Ags immune complexes in glomeruli
  15. Culture and Identification Group A streptococci
    • -Readily grown on BAP
    • -Beta (occasionally non hemolytic)
    • -Identified (presumptive) with sensitivity to antibiotic bacitracin
    •      -Other betas are resistant
  16. Group B Strep: S. agalactiae Epidemiology
    • Commensal human GI and 10-30% of healthy women
    • Diseases
    • -Neonatal: early onset: Pneumonia from
    • inhaled amniotic fluids/vaginal secretions during birth
    • -Late onset: Intestinal infection,
    • sepsis and meningitis
    • -Postpartum: Mastitis, endometritis,
    • sepsis, meningitis
  17. Lab Identification and Growth
    • -Readily grown overnight on BAP, beta zone
    • -Resistant to bacitracin
    • -Capable of hydrolysis of hippurate, other strep cannot do this
  18. Streptococcus pneumoniae Infections and Disease
    • -Carriage:5-75% depending on time of year/age
    • -Pneumonia:100,000 cases a year, 40,000 deaths
    • -Otitis media:most common cause for visit to pediatrician -Meningitis, sepsis, severe disease
  19. Strept. pneumoniae Capsular polysaccharide
    • -inhibits complement lysis, antibody binding, phagocytosis, > capsule serotypes
    • -Capsular serotype change via cassette type mechanism of genetic recombination
  20. Strep. pneumoniae Pneumococcal surface
    • -PspA: coiled-coil protein
    •     -Bound to choline on bacterial polysaccharides (teichoic/lipoteichoic)
    •     -Inhibits complement lysis
    •     -antibodies to PspA are protective
    •     -many, many serotypes
    • - Other Choline binding proteins (CBPs)
    •     -8-14
    •     -cbpA mutant showed reduced adherence
  21. Strept. pneumoniae virulence mechanism
    • -Pnemolysin
    •      -pore-forming toxin
    •      -Binds Fc of IgG, fixes complement
    •      -Limits inflammatory response
    •      -released by autolysin
    • -IgA protease
    •      -cleaves IgA
    • -Teichoic acid/Lipoteichoic acid:
    •      -Surface polysaccharide carrying phosphorylcholine
    •      -Potentially
    • involved in adherence and invasion
    • -Autolysin
    •      -Division of daughter cells
    •      -Lysis of bacteria in stationary phase
    •      -Release of pneumolysin and possibly other virulence factors
    •      -Autolysin mutants are reduced in virulence in the mouse model
  22. S. pnumoniae Variation: Transformation
    • -Population structure is panmictic (non-clonal)
    • -Pneumococci undergo transformation at high frequency (+95%)
    • -Occurs at late log  phase
    • -Is induced by a secreted peptide (competence factor)
  23. S. pneumoniae: Phase Variation
    • -18% of pneumococcal genes are predicted to phase-vary
    • -Vary between opaque and translucent
    •        -Transparent less virulent
  24. Growth and Laboratory Identification of S. pneumoniae
    • -Readily grown in laboratory
    • -Forms large gooey colonies
    •      -Exhibit alpha hemolysis
    • -Identified by sensitivity to compound Optochin
    • -Serological identification not routine
  25. Most common source of vaccine preventable death in children
    S. pneumoniae
  26. Polysaccharide vaccine for S. pneumoniae
    • -23-valent vaccine available, contains
    • mixture of most common types of capsular polysaccharides
    • -Conjugate vaccine
    •       -2000: 7-valent
    •       -2009: 10-valent
    •       -2010: 13-valent
    • -Implementation of 7-valent vaccine
    • has changed most common serotype to non-7VPCV