Lab 2

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  1. What do Gram-negative organisms frequently inhibit?
    Gram-positive organisms when they are cultivated together.
  2. What do you do when looking for staphylococci or streptococci?
    Streak the unkown mixture onto a selective medium that inhibits Gram-Negative growth.
  3. What does the Phenylethy Alcohol Agar do?
    Selective medium the encourages the growth of Gram-positive organisms and inhibits the growth of most Gram-negative organisms.
  4. Is pea  a differential medium?
    No, selective
  5. What does sodium chloride provide?
    A stable osmotic environment that is suitable for the additon of sheep blood
  6. How does phenylethy alchohol work?
    breaks doen gram negative by breaking down their membrane permeability barrier.
  7. What does Mannitol salt agar contain?
    Carbohydrate mannitol, sodium chloride and a ph indicator red.
  8. phenol red ph
    • yellow below 6.8
    • red at 7.4 to 8.4
    • pink at 8.4
  9. What does mannitol provide?
    Substrate for fermentation and makes the medium differential.
  10. What does sodium chloride do?
    makes the medium selective because its concentration is high enough to dehydrate and kill most bacteria
  11. What indicates whether fermentation has taken place?
    by changing color as the pH changes.
  12. Do mannitol salt agar able to ferment?
    no, the growth appears pink or red and the medium remains unchanged
  13. What ferments the mannitol?
    Staphylococcus aureus, produces acids and lowers the pH of the medium resulting in a bright yellow colonies usually surrounded by a yellow halo.
  14. What is Mannitol Salt Agar used for?
    Isolation and differentiation of Staphylococcus aureus.
  15. What is the application of the Phelyethyl Alchohol used for?
    to isolate staphylococci and streptococci from specimens containing mixtures of bacterial flora screening out the common contaminatns Escherichia coli and proteus species.
  16. What is a MacConkey Agar?
    A selective and differential medium containing lactose, bile salts, neutral red, and crystal violet.
  17. In a MacConkey Agar, what inhibits growth of Gram-positive bacteria?
    Bile salts and crystal violet.
  18. Neutral red dye is a pH indicator that is colorless at what pH and red at what pH.
    above 6.8 and less than 6.8
  19. What doe sthe Acid accumulating from lactose fermentation do?
    Turn the dy red.
  20. What do the formulations without the crystal violet allow the growth of?
    Enterococcus and some species of Staphylococcus, which ferment the lactose and appear pink on the medium.
  21. What bacteria ferment the lactose? What color do they appear on the medium?
    • Enterococcus and staphylococcus.
    • Pink
  22. What is the main purpose of the MacConkey Agar?
    to isolate and differentiate members of the Enterobacteriaceae based on the ability to ferment lactose.
  23. Eosin Methylene Blue Agar is selective or differential?
  24. What does Eosin Methylene Blue Agar contain?
  25. What does Emb Agar used for?
    isolation of fecal coliforms
  26. What is Hektoen Enteric Agar used for?
    Moderately selective and differential medium designed to isolate Salmonella and Shigella species from other enterics.
  27. What are the bile salts included for?
    precvent or inhibit growth of Gram-bositive organisms.
  28. What are the Bromthymol blue and acid fuchsin dyes are added to indicate?
    pH changes.
Card Set:
Lab 2
2013-10-09 05:51:53
Selective Media Isolation Gram Positive Cocci

Selective Media for isolation of gram-positive cocci
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