Microbiology: Voges-Proskauer Test — Transcript

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1. 0:00my name is Kevin toke off in this video
2. 0:02we're going to discuss the theory behind
3. 0:03the Volks / scour test alright
4. 0:06so let's go over some basics of
5. 0:08bacterial metabolism that you may not
6. 0:10have seen yet we know glucose can be
7. 0:13converted to pyruvic acid through the
8. 0:14process of glycolysis when we looked at
9. 0:18the methyl red test that pyruvic acid
10. 0:21could be converted to mixed organic
11. 0:22acids and if it turned red it was going
12. 0:25to be a positive methyl red test now the
13. 0:28Volks / scour test is looking at
14. 0:30something a little bit different it
15. 0:32turns out that pyruvic acid can be
16. 0:34converted ultimately through a series of
17. 0:36two enzymes to a molecule called asset
18. 0:39Owen now acetone is not directly what
19. 0:43we're measuring but it turns out that
20. 0:45acetone is involved in a series of
21. 0:47metabolic transformations we can form
22. 0:50various compounds like dials or Dione's
23. 0:54now if we have bacteria that can produce
24. 0:58acetone what we can actually do is put
25. 1:02in a series of reagents and we can
26. 1:04actually convert the acetone in the
27. 1:07absence of enzymes to a dye own called a
28. 1:10diacetyl and it turns out that diacetyl
29. 1:13can react with pep tones specifically
30. 1:15arginine residues of pep tones to
31. 1:18produce a red color okay so how do we do
32. 1:23that well it turns out that acetone if
33. 1:24we throw in Alphen at full amine which
34. 1:27we've seen before
35. 1:28and potassium hydroxide with oxygen gas
36. 1:32it turns out that acetone can be
37. 1:35converted without the need for an enzyme
38. 1:36into this dye own called diacetyl now in
39. 1:40this mixture we also have pep tones and
40. 1:43pep tones contain arginine residues this
41. 1:46is an arginine amino acid that's part of
42. 1:48the peptone it turns out if the arginine
43. 1:50can react with the diacetyl and when it
44. 1:53does we have a color change that is red
45. 1:56now basically what the Volks press our
46. 1:59test is measuring is the ability of
47. 2:01bacteria to convert glucose into neutral
48. 2:06end products okay diacetyl and
49. 2:10butanediol are both neutral
50. 2:12products however we're specifically
51. 2:15reacting these reagents with the asset
52. 2:17Owen because the acetone is indicative
53. 2:20of its ability to convert glucose to
54. 2:22neutral end products okay and a red
55. 2:25color change would be VOC spur Scour
56. 2:27positive okay here's some specific
57. 2:31results what they might look like very
58. 2:33similar to the methyl red test if we see
59. 2:35usually towards the top of the tube if
60. 2:39we have a red color or sometimes it can
61. 2:42go darker a little bit purplish that's
62. 2:44going to be a positive VOC spur scour
63. 2:45test that means that the bacteria are
64. 2:47able to convert glucose into these
65. 2:50neutral end products such as acetone and
66. 2:52dials and Dione's okay you can see a
67. 2:56positive result right here as well as
68. 2:58over here if we don't see that reddish
69. 3:00purple color change such as over here or
70. 3:03on this side over here that's a negative
71. 3:06result and so the bacteria do not have
72. 3:08this ability okay and also understand
73. 3:12this because it can help you tie things
74. 3:13together when you're tested on it the
75. 3:16results of the Voges persk our test is
76. 3:18red red color change that we typically
77. 3:21see towards the top is very similar to
78. 3:24the results of the methyl red test that
79. 3:27we looked at in another video so you
80. 3:29kind of just remember for VOC spur scour
81. 3:31and methyl red we want to see a red
82. 3:33color for positive for whatever they're
83. 3:35measuring then that might help you a
84. 3:38little bit although what they're
85. 3:40measuring is a little bit different
86. 3:41methyl red was testing ability to
87. 3:44convert pyruvic acid to mixed organic
88. 3:46acids so acids we're exposed Bogues /
89. 3:49scour is measuring the ability to
90. 3:51convert glucose into neutral end
91. 3:53products rather acidic rather than
92. 3:55acidic ones okay and again I'll mention
93. 3:58this as I've mentioned in the previous
94. 4:00videos this is another one of the
95. 4:01techniques that we're going to use to
96. 4:03differentiate between gram-negative
97. 4:05bacillus okay make sure to watch the
98. 4:08demonstration video on the Volks / scour
99. 4:10test