bile esculin test

  1. presumptive identification of an organism
    Presumptive identification of microorganisms is defined as identification by the colony morphology, growth on selective media, gram stains, or up to three tests 

    This test is used most commonly for presumptive identifi- cation of enterococci and members of the Streptococcus bovis group, all of which are positive.
  2. Which organism does this test identify?
    Members of Streptococcus and Enterococcus genus
  3. How is an organism identified by this test?
    The carbohydrate esculin (substrate) is hydrolized
  4. What are the ingredients in bile esculin agar slants?
    bile saltsesculinferric ammonium citratebeef and gelatin extracts
  5. Describe the reactions which lead to the black precipitate.
    Hydrolyze the carbohydrate esculin in the presence of bile Produce glucose and esculetin Esculetin reacts with ferric ammonium citrate Form a blackish precipitate
  6. What causes the black precipitate?
    The esculetin end-product reacts with ferric citrate forming phenolic iron complexturning the slant dark to black brown
  7. How much of the tube must contain black precipitate to be considered a positive reaction for esculin hydrolysis?
    50% or greater
  8. Is the Bile Esculin test for Gram + or Gram - organisms?
    Gram +, specifically the Streptococcus genus and Enterococcus genus
  9. BE
    Selective, undefined, and differential-tests the ability of organisms to hydrolize esculin in the presence of bile-Selective ingredient=bile-Differential ingredient=esculin
  10. Organisms capable of hydrolyzing esculin in the presence of bile
    -Enterococcus faecalis (pathogenic)-Lactobacillus casei (nonpathogenic)
  11. esculin is an example of a type of molecule known as glycoside its 2 components are the ____ and ___
    glucose and esculetin
  12. the bile inhibits the growth of most ___ organisms
  13. what is the source of bile in bile esculin agar
  14. when esculin molecules are split by bacteria ___ reatcs with ferric citrate and forms a ___ color phenolic iron complex
    • 1.esculetin
  15. describe the positive result including time frame
    48 hours enterococculus faccalis is positive and turns esculin into esculetin. The esculitin reacts with iron and produces a black color giving a positve
  16. describe a negative result in this experiment
    citrobacter freundii is negative because it cant hydrolyze esculin
  17. explain how bile esculin agar acts as a differential medium
    it acts a a differential medium because it contains feeric ammonium citrate to produce the black color then the bile inhibits the growth of a negative
  18. explain how bile esculin agar acts as a selective medium
    the bile inhibits growth for for others and it has a specialized growth for a positive result
  19. explain how the ferric citrate in bile esculin agar allows you to observe a positive result
    the ferric citrate reacts with the esculin to produce a black color and the bile inhibits the growth of the negative c. freundii
  20. exoenzyme
    is an enzyme produced by a cell that catalyze reactions outside of the cell
  21. endoenzyme
    is an enzyme produced by a cell that catalyze reactions inside the cell
Card Set
bile esculin test
bile esculin test