Microbiology: Indole Test (Tryptophanase) — Transcript

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1. 0:00my name is Kevin toke off and in this
2. 0:01video we're gonna discuss the theory
3. 0:03behind the indole test the indole test
4. 0:06is another test that's used for the
5. 0:08identification of gram-negative bacilli
6. 0:10along with several others such as methyl
7. 0:12red and Vogue's per Scour okay we'll
8. 0:16talk about those in other videos here's
9. 0:18the basic theory behind the indole test
10. 0:20we have an amino acid called tryptophan
11. 0:23it turns out that some bacteria Express
12. 0:27an enzyme called tryptophan ace and
13. 0:29tryptophan ace basically is able to
14. 0:32hydrolyze tryptophan into ammonia in
15. 0:37dull and pyruvic acid or pyruvate now it
16. 0:42turns out that if we add a reagent
17. 0:44called Kovacs reagent Kovacs reagent
18. 0:48will react with this indole product but
19. 0:51not tryptophan it'll only react with
20. 0:52indle and it will turn a red color which
21. 0:56will actually appear in near the top of
22. 0:58the tube that you can see that right
23. 1:01here here we have an indole positive
24. 1:03result so an envelope aza t'v result is
25. 1:06indicative that the enzyme tryptophan
26. 1:08ace is expressed by the bacteria okay
27. 1:12so as long as tryptophan ace is present
28. 1:15tryptophan will be hydrolyzed into
29. 1:17ammonia in Dole and pyruvic acid and
30. 1:19Kovacs reagent can react with indole to
31. 1:22produce this red color near the top of
32. 1:24the tube if we don't see a red color so
33. 1:27if we stood like a yellowish color near
34. 1:29the top that means that the test is
35. 1:31negative for indle and therefore the
36. 1:34enzyme tryptophan ace is not expressed
37. 1:36by those bacteria okay let's take
38. 1:39another look at the results of the indle
39. 1:41test alright so remember if as long as
40. 1:44we produce in dole it will react with
41. 1:46Kovacs reagent and we'll see a red color
42. 1:49this is the same image from the previous
43. 1:51slide here's another look at this
44. 1:53sometimes it can be a little bit darker
45. 1:55but it should be pretty obvious whenever
46. 1:58you have a reaction with Kovacs reagent
47. 2:01it will definitely not be this yellowish
48. 2:03green or yellow whatever so over here
49. 2:05this would be a positive in dole result
50. 2:08meaning that the bacteria here actually
51. 2:10do Express tryptophan ace
52. 2:13okay over here just like over here this
53. 2:16is a negative indle result meaning the
54. 2:18bacteria does not express tryptophan
55. 2:21base okay
56. 2:22so overall the end-all test is a fairly
57. 2:25straightforward simple test to interpret
58. 2:28as long as you produce indole Kovaks
59. 2:31reagent will produce that red purplish
60. 2:33color usually red near the top of the
61. 2:36tube all right make sure to watch the
62. 2:40demonstration on this video as well
63. 2:42thank you