microlab exam 2

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microlab exam 2
2012-11-06 19:07:47

exam 2 microlab critical thinking questions
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  1. What is the component in the SIM deep tubes that makes this medium suitable to detect the production of indole by bacteria?
  2. What organic molecule is necessary to detect mixed acid fermentation by bacteria?
    methyl red
  3. why is a chemically defined medium necessary for the detection of citrate utilization by bacteria
    because the citrate converts to CO2 and if the proper medium insn't there for sodium to bind and oxygen to be used, it will simply escape and you won't be able to tell
  4. Indole test uses what to detect ph
    kovacs reagent
  5. medium for methyl red test
  6. medium fo rvoges proskauer test
    glucose, o2
  7. medium for citrate teset
    sodium citrate, o2
  8. what is the importance of catalase to certain bacteria?
    catalyzes the destruction of peroxide
  9. do anaerobic bacteria require catalse? explain
    strict ones don't because there is not o2 present to generate the toxins
  10. what is the substrate of the catalase reaction?
    hydrogen peroxide
  11. what metabolic property characterizes bactera that posses oxidase activity?
    cytochrome oxidase
  12. Do anaerobic bacteria require oxidase? explain
    no because they don't use o2
  13. what is the function of the test reagen in the oxidase test
    it acts as an artificial substrate getting oxidized by cytochrome oxidase
  14. the oxidase test is used to differentiate amound which groups of bacteria
    those that use oxidase and those that don't
  15. what is the purpose of the phenol red in the urea broth medium
    detects the ph of the medium
  16. when would you use the urease testq
    to find bacteria that passes the enzyme urease.
  17. why does the urea disk change color
    increase in ammonia cause the phenol red to change color since ammonia is alkaline
  18. what is the urea broth
    a medium with urea and phenol red
  19. explain what occurs during decarboxylation
    decarboxylase enzyme removes a carboxyl group from an organic molecule and produces an amine with co2
  20. why does the LDC broth or lysine iron agar turn purple when lysine is decarboxylated
    the decarboxylase enzyme turns the lysin into an amine and neutralises the ph
  21. why does the LDC medium always turn yellow regardless of the ability of the bacteria to produce lysine decarboxylase
    because the fermentation of glucose raises the ph of the medium turning it yellow
  22. why is the lysine decarboxlase tset negative if both LDC and DC broths turn purple
    because it cannot be proven that the purple color is due to lysine being used
  23. why is sterile mineral oil added to LDC test media
    to preven O2 from reacting with the medium
  24. how does the pH indicator bromcresol purple indicate a change in ph
    by chaning from yellow to purple or vice versa
  25. what is the purpose of the ferric chloride in the phenylaline deamination test
    it reacts iwth phenylpyruvic acid which is the product of phenylaamine danimation
  26. name some bacteria that can deaminate phenylalanine
    p. vulgarus, proteus, morganella, providencia
  27. describe the process of deamination
    the enzyme catalyzes the removal of an amino group from phenylalanine. this produces orgainc acids water and ammonia
  28. describe the color of an uninoculated tube of phenlalanine agar
  29. from your results which bacteria are negative for nitrate reduction? which are positive?
    Negative are s. epidermus. all the others are positvie
  30. why is the development of a red color a negative test when zinc is added?
    because the zinc reacts with the no2 to push it back to no3
  31. how would you perform a complete test for the presence of nitrate reduction?
    ad the a and b and then zince to see if it changes back