Carbohydrate (CHO) Fermentation [Durham Tube Test] — Transcript

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1. 0:04[Music]
2. 0:08welcome back to microbiology lab my name
3. 0:11is Kevin tow cough please make sure to
4. 0:12like this video and subscribe to my
5. 0:14channel for future videos and
6. 0:16notifications in this video we're gonna
7. 0:18discuss what's called the a carbohydrate
8. 0:20fermentation test now here's some images
9. 0:23of the actual results of a carbohydrate
10. 0:24fermentation test I'll explain what the
11. 0:27test does in a minute but let's actually
12. 0:29look at this setup because it actually
13. 0:31looks a little bit different what you'll
14. 0:33see here is actually inside a larger
15. 0:35test tube it appears we have an inverted
16. 0:38smaller test tube that's sitting inside
17. 0:40the broth and that's exactly what it is
18. 0:42so in a carbohydrate fermentation test
19. 0:44which is actually sometimes called just
20. 0:46the Durham tube test we have here a
21. 0:49large test tube okay it clearly has some
22. 0:52broth in it we'll discuss that in a
23. 0:53minute and then I have what looks like
24. 0:55and it kind of is it's called a Durham
25. 0:57tube but it's a smaller test tube much
26. 1:00thinner and it's shorter and it's
27. 1:02actually inverted so actually you turn
28. 1:04it upside down and just stick it into
29. 1:05the broth so the opening of the Durham
30. 1:07tube is actually down here on the bottom
31. 1:08so right down here where my mouse is
32. 1:11that's the opening and so that allows
33. 1:12the broth to go up into the Durham tube
34. 1:14okay and that's the setup alright so in
35. 1:18the broth there's one sugar and we can
36. 1:21use any sugar but it's just one at a
37. 1:23time here's some listed that we can use
38. 1:26we can use glucose lactose sucrose nanos
39. 1:30glycerol there's others we can use any
40. 1:33that you can think of
41. 1:34now glycerol is not technically a sugar
42. 1:36it's not a carbohydrate but it's
43. 1:38actually linked with glycolysis and it
44. 1:39turns out you can actually do this test
45. 1:41with glycerol and it can actually be
46. 1:43useful in some cases but there's one of
47. 1:45those molecules inside this broth right
48. 1:50now as the name suggests carbohydrate
49. 1:53fermentation tests determine whether or
50. 1:55not a bacteria is able to ferment one of
51. 1:58these sugars so for example if we put
52. 2:01mannose in here then that test would
53. 2:05determine whether or not that bacteria
54. 2:06could ferment mannose if we put lactose
55. 2:09in here it would determine whether or
56. 2:11not those bacteria confirm it
57. 2:13okay so it's just one at a time and
58. 2:16remember what fermentation is generally
59. 2:18speaking it's a metabolic process that
60. 2:20consumes sugar and generates energy the
61. 2:23process normally does not require oxygen
62. 2:24so it's considered anaerobic and it
63. 2:28normally is gonna release a lot of heat
64. 2:29okay and in some cases this is important
65. 2:32to realize it can actually release gases
66. 2:35okay that's going to be important in one
67. 2:38of the results here actually the middle
68. 2:39one so now let's actually go into
69. 2:41interpreting the results so hopefully
70. 2:43you understand what's in here all right
71. 2:46so let's take for an example let's do is
72. 2:48a man else as an example let's say that
73. 2:50this broth contains mannose all right so
74. 2:53we have mono soon here and we inoculate
75. 2:56it using a simple broth inoculation we
76. 2:58incubate it and it turns all yellow like
77. 3:01this on the on the Left okay that's
78. 3:05gonna indicate a positive result now
79. 3:07unlike most tests we don't just put a
80. 3:09positive sign okay the correct way to
81. 3:12actually indicate that this is a
82. 3:13positive result is to put an A now why
83. 3:16is that inside the broth there's also a
84. 3:19pH indicator most of the time it's
85. 3:21phenol red okay when phenol red becomes
86. 3:26acidic when it becomes acidic the pH
87. 3:29gets lowered and the pH indicator turns
88. 3:32yellow okay really what the bacteria are
89. 3:36doing is they're converting these sugars
90. 3:38into more acid end products such as
91. 3:41lactic acid very similar to what we saw
92. 3:44in the macconkey agar which i showed you
93. 3:46in the previous video and so when the pH
94. 3:49goes down during the fermentation it
95. 3:51turns the pH indicator yellow so a
96. 3:54yellow result means it's positive okay
97. 3:57and if it's all yellow like this we put
98. 4:00a four acidic okay the a stands for
99. 4:03acidic but that's the case when it turns
100. 4:05yellow all right now notice here this is
101. 4:08important not only is the broth down
102. 4:09here yellow in the base but also going
103. 4:12up the Durham tube right up to the very
104. 4:14tip of the Durham tube right here it's
105. 4:15all yellow when you have that yes it's a
106. 4:19positive reaction but it just gets the
107. 4:20letter A all right so hopefully that
108. 4:23makes sense now go into the middle case
109. 4:26right here
110. 4:27as I mentioned here in this bullet point
111. 4:29some bacteria with some sugars they can
112. 4:32both ferment the sugar into an acid end
113. 4:34product such as lactic acid and they can
114. 4:37produce gas at the same time that's what
115. 4:39concomitant lait means okay so in this
116. 4:43case notice at the top of the Durham
117. 4:45tube you see the liquid meniscus right
118. 4:47here but then there's a space here
119. 4:49here's the top of the Durham tube where
120. 4:51the tip of my mouse is you see there's
121. 4:53some space here where there's no fluid
122. 4:54at all no liquid okay that space is
123. 4:58filled with gas so this situation in the
124. 5:01middle looks almost identical to here on
125. 5:03the left except for there's gas here
126. 5:06it's still all yellow at least any place
127. 5:08where the fluid is it's all yellow so it
128. 5:11gets an A but we have to put a G for
129. 5:13guess okay and that just means that
130. 5:16right up here at the top of the Durham
131. 5:18tube there's some gas okay that's the
132. 5:20only place you'll ever see the gas so
133. 5:22just look here right in the top of the
134. 5:24Durham - um sometimes you'll see a / G
135. 5:27like this sometimes you can see a comma
136. 5:30G or just a G for the purpose of my
137. 5:32class I don't care how you put it as
138. 5:34long as there's an A in a G okay but
139. 5:37that's the case when you have when
140. 5:39you're positive for fermentation and you
141. 5:41have gas again we don't put a positive
142. 5:43sign we put a + G that's just typically
143. 5:46how we do it alright so what about a
144. 5:50negative reaction right now this
145. 5:52indicates right here our control so it's
146. 5:54uh Nanaki elated but generally you'll
147. 5:56have a result that looks very similar to
148. 5:58this now in this negative reaction right
149. 6:01here it's all red okay the fluid in the
150. 6:05broth is red the fluid in the Durham
151. 6:07tube is red anytime you have a situation
152. 6:11where there's any red whatsoever any red
153. 6:14in this case it's all red but any red
154. 6:16it's automatically negative now for a
155. 6:19negative reaction we do indicate a
156. 6:21negative sign I don't have the negative
157. 6:23sign here I just got this image off of
158. 6:24Google but if if you were to see this
159. 6:27experimentally after inoculating you
160. 6:29would actually just write a negative
161. 6:30sign that's all you do so your results
162. 6:32are a AG and negative sign now when I
163. 6:37say any red means negative you can
164. 6:39sometimes have city
165. 6:40were the broth in here is red but in the
166. 6:44Durham tube it's yellow the yellow
167. 6:47doesn't make it positive the fact that
168. 6:49there's red in the broth any red
169. 6:51whatsoever means it's automatically
170. 6:53negative okay that's very important to
171. 6:56understand and even if the situation
172. 6:57were flipped and it was red in the tube
173. 7:02the Durham tube that is and yellow in
174. 7:04the base here of the main test tube that
175. 7:06would still be negative because there's
176. 7:08red so the point here is any red I don't
177. 7:11care how much red it's automatically
178. 7:13negative that's what we're gonna say and
179. 7:15so that being said there's really three
180. 7:17results you can have any red any red
181. 7:20whatsoever it's automatically negative
182. 7:22or if it's all yellow and no gas up here
183. 7:26it's just a if you have it all yellow
184. 7:29but then there's a little space up here
185. 7:31where there's gas in the tip of the
186. 7:32Durham tube it's AG G for gas three
187. 7:36results okay and again in our example
188. 7:39where this broth was filled with mannose
189. 7:41in this case over here and what we'd say
190. 7:44yes that bacteria Furman's mannose a in
191. 7:47the middle here yes that bacteria
192. 7:49ferment smells but it also produces gas
193. 7:51in the process a G over here on the
194. 7:53right this bacteria does not ferment
195. 7:56mannose at all okay that's the
196. 7:58interpretation and hopefully this test
197. 8:01makes sense to you it's pretty simple
198. 8:03the only thing you really have to
199. 8:05memorize in terms of the results is the
200. 8:06a the a G and negative all right please
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