Gram Positive Media

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Gram Positive Media
2013-01-29 22:58:21
Microbiology Three

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  1. What are the two types of agar we use for gram positive media?
    • blood agar
    • mannitol salt agar
  2. What is a blood agar?  What blood is commonly used and why?
    • enriched media
    • supports growth of most bacterial pathogens
    • sheep blood commonly used due to the hemolytic action by some bacteria on the RBCs
  3. What is hemolysin?
    • a substance (enzyme) produced by some bacterial cells
    • digests RBCs
    • pathogenic
  4. What are the 4 types of hemolysis in a blood agar?
    • alpha
    • beta
    • gamma
    • delta
  5. What is alpha hemolysis?  What does it look like?
    • partial hemolysis
    • narrow band of greenish or slimy discoloration around the bacterial colonies
  6. What is beta hemolysis?  What does it look like?
    • complete hemolysis
    • creates a clear zone around the bacterial colony
  7. What is gamma hemolysis?  What does it look like?
    • produces no chance in the appearance of the media
    • no hemolysis around colonies
  8. What is delta hemolysis?  What does it look like?
    • double-zone hemolysis
    • zone of hemolysis surrounded by a narrow zone of hemolysis around a bacterial colony
  9. What is mannitol salt agar used for?
    • selective media for Staphylococci
    • high salt concentrations inhibits most other bacteria
  10. What is mannitol?
  11. What gives the mannitol salt agar the red appearance?
    phenol red
  12. In the presence of acid, the phenol red turns _____.  This indicates which type of bacteria?
    • yellow
    • Staphylococcus aureus
  13. What happens to the mannitol salt agar if there is Staphylococcus epidermidis?
    does not ferment mannitol and media will stay red