Blood Agar

  1. hemolysins:
    • exotoxins produced by gram-positive cocci species
    • able to destroy red blood cells & hemoglobin
  2. Blood agar is sometimes called? why?
    • Sheep blood agar
    • because it contains 5% sheep blood in tryptic soy agar base
  3. 3 major types of hemolysis are:
    • beta-hemolysis
    • alpha-hemolysis
    • gamma-hemolysis
  4. beta-hemolysis:
    complete destruction of RBC's and hemoglobin, results in a clearing of the medium around the colonies
  5. alpha-hemolysis:
    pratial destruction of RBC's and produces a greenish discoloration of the agar around the colonies
  6. gamma-hemolysis:
    non-hemolysis and appears as simple growth with no change to the medium
  7. hemolysins produced by sreptococci are called? what are their 2 forms?
    • streptolysins
    • types: O & S
  8. Streptolysin O:
    • oxygen labile
    • expresses maximal activity under anaerobic conditions
  9. Streptolysin S:
    • oxygen-stable
    • express itself optimally under anearobic conditions
  10. streak stab technique:
    • easiest method of providing an enviroment favorable for streptolysisns on blood agar
    • plate is streaked for isolation and stabbed
    • stab encourages streptolysin activity because of the reduced oxygen concntration of the subsurface enviro
  11. blood agar is used for isolation and cultivation of many types of? differentiates?
    • fastidious bacteria
    • based on hemolytic characteristics, especilly w/in streptococcus, enterococcus and aerococcus.
  12. Blood Agar Results:
    clearing around growth
    greening around growth
    No change in the medium
    • organisms hemolyzes RBC's completely (beta)
    • organism hemolyzes RBC's partially (alpha)
    • Organism does not hemolyze RBC's (gamma)
Card Set
Blood Agar
Blood Agar