MMI 302: Streptococcus

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MMI 302: Streptococcus
2013-11-19 13:18:34
MMI 302

MMI 302
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  1. Historical classification of strep:
    Based on hemolytic properties, not good, several species show same hemolytics
  2. Who pioneered Strep. serology
    • Rebecca Lancefield
    • Found most strep had unique cell wall carbohydrates
  3. Strep classification based on serology
    • Now in C-groups (carbohydrate antigens)
    • Group A: Strep. pyogenes
    • Group B: Strep. agalactiae
    • Strep. pneumoniae has no C-group
  4. Strep shapes:
    Round, oval or pointed
  5. How do strep divide
    On one plane
  6. Morphology of Strep. pneumoniae
    lancet-shape, diplococci
  7. Rapid Oxidase test:
    • Used to differentiate gram + cocci
    • Colorometric assay for cytochrome C oxidase
    • Differentiates micrococcus (positive) from Strep/Staph (neg)
  8. Bacitracin sensitivity
    Micrococcus sensitive, Staph resilient
  9. Hemolytic toxins in Strep. pyogenes
    • Both are beta, called Streptolysins
    • Streptolysin S (SLS): O2 stable, hemolysis on surface, not antigenic
    • Streptolysin O (SLO): O2 labile, hemolysis on subsurface, antigenic
    • Need to stab BAP when doing throat culture because the O2 labile SLO strep will show no hemolysis on surface where O2 destroys toxin
  10. Differentiating alpha-hemolytics
    S. pneumoniae can be identified out of the group by sensitivity to optichin, other alpha-hemos are resistent
  11. Disease caused by beta-hemolytics
    • Group A, pyogenes
    • Pharyngitis, Pyodermas (pyogenic skin diseases): Cellulitis, fasciitis, impetigo
    • Necrotizing fasciitis (mortality 20%)
  12. Post-streptococcal infections caused by group A, pyogenes
    • Rheumatic Fever, acute glomerulonephritis
    • Example of sequelae: abnormal condition following/resulting from infection, disease or injury.
    • Is often autoimmune
  13. Rheumatic Fever:
    • In 5-15 year olds, rarely after 18 y.o
    • Occurs 14-28 days after strep throat/scarlet fever
    • Due to anti-strep antibody interaction w/ heart tissue, example of molecular mimicry w/ type II hypersensitivity reaction damaging tissues
  14. Acute glomerulonephritis
    • Post-strep disease
    • Inflammation of blood vessels in kidneys
    • prevents proper filtration
  15. Streptococci as normal microbiota
    • Carriers: harbor pathogenic species w/ no obvious disease
    • Disease is from new strain
    • S. pyogenes only found in humans
  16. Group B, S. agalactiae infections
    • Neonatal:
    • Stillbirth (ascending from vagina)
    • Leading cause of neonatal meningitis and sepsis
    • Early onset is from birth canal
    • Late onset is from nosocomial spread
    • Can also cause a low percentage of UTI in adult female
  17. Group C streps
    • zooepidemicus, equisimilis, equi
    • Mostly veterinary pathogens, can infect humans
  18. Diseases caused by non-beta hemolytics
  19. Hemolytics and their species:
    • Alpha Hemolysis: Pneumoniae and viridans
    • Beta Hemolysis:
    • Group A: Pyogenes
    • Group B: Agalactaie
    • Group C: equi and such

    Non-hemolytic: Enterococci
  20. Enterococcus
    • Ex: Faecalis and faecium
    • Group D "strep"
    • Non-hemolytic
    • Found in GI tract, bile-resistent
    • Cause UTI, Bacteremia, Wound infection
    • Nosocomial spread
  21. Strep. pneumoniae colony types
    Mucoid strains --> more capsule produced/autolysis occurs in center of colony, concave "doughnut" shape
  22. Diseases from Strep. pneumoniae
    Community acquired: bacterial pneumonia, bacterial meningitis, otitis media, sinusitis, conjunctivitis
  23. Viridans Strep. specie s
    • Alpha-hemolysis
    • S. mutans: dental caries, tooth decay, can make up 50-60% of plaque
    • Can lead to bacterial endocarditis