Microbiology: Coagulase Test — Transcript

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1. 0:00my name is Kevin tow cough and in this
2. 0:01video we're going to discuss the theory
3. 0:03behind the coagulase test so first of
4. 0:06all let's discuss some very basic
5. 0:08physiology so in your blood right now
6. 0:10you have soluble fibrinogen and
7. 0:13fibrinogen is an inactive protein and we
8. 0:16know that whenever we have tissue
9. 0:18injuries such as a cut like on your arm
10. 0:20your blood clots and you would actually
11. 0:23see over the course of maybe a couple
12. 0:26minutes you see basically as we say in
13. 0:28layman's terms your blood dries that's
14. 0:31because whenever you have tissue injury
15. 0:33and only when there's tissue injury you
16. 0:36have a series of enzymes called clotting
17. 0:38factors that become activated and they
18. 0:40ultimately convert the soluble fiber
19. 0:43imogen protein into a fibrin clot okay
20. 0:47and the beauty of this system is that
21. 0:51this conversion of fibrinogen to fibrin
22. 0:53should only occur when there is tissue
23. 0:56injury however Staphylococcus aureus
24. 1:00which is the most significant pathogen
25. 1:03of the Staphylococcus genus um can
26. 1:06express an enzyme called coagulase and
27. 1:09this can cause blood clots
28. 1:11even without tissue injury and
29. 1:13coagulates the enzyme is actually part
30. 1:16of how this Staphylococcus aureus
31. 1:18propagates it's pathogenic effects in
32. 1:20vivo okay so the basis behind this is
33. 1:24we're going to use have a have some kind
34. 1:26of tube and then we're gonna have plasma
35. 1:28okay we don't use whole blood so our
36. 1:32results will not appear red we're only
37. 1:34using the plasma part which doesn't have
38. 1:36the red blood cells the plasma is going
39. 1:39to be inoculated with some kind of
40. 1:41bacteria if we do Staphylococcus aureus
41. 1:44and it's coagulates positive what we
42. 1:46should see is because of the clotting
43. 1:48process that is the conversion of
44. 1:50fibrinogen to fibrin we should actually
45. 1:52see some kind of visible clumps of the
46. 1:55bacteria together because they're
47. 1:56getting caught in the clock itself all
48. 1:59right let's think about something for a
49. 2:00second if I have a test tube and say I
50. 2:02just fill it with water okay and I take
51. 2:05that test tube and tilt it like this we
52. 2:08know from intuition just living that the
53. 2:10water should probably end up like this
54. 2:13okay it shouldn't look like this down
55. 2:16here okay
56. 2:17this wood might be if the water was like
57. 2:19frozen or something like that okay so
58. 2:21what we do is we take plasma not whole
59. 2:24blood whole blood has red blood cells in
60. 2:27it and so because we're only using the
61. 2:29plasma our actual results will actually
62. 2:32be not red there'll be more of a tan
63. 2:34color okay theoretically and we're gonna
64. 2:37inoculate the plasma with some kind of
65. 2:39bacteria one of the examples of a
66. 2:41bacteria that expresses coagulase is
67. 2:44some members of Staphylococcus aureus
68. 2:46okay and we may see blood clots okay now
69. 2:52these two results down here are
70. 2:54coagulates positive meaning these
71. 2:56bacteria whatever we're in here express
72. 2:59the enzyme coagulase and it can appear
73. 3:01like one of two things this one on the
74. 3:03bottom would be if the entire fluid here
75. 3:07actually clotted okay now notice it's
76. 3:10not like this where we turn it on its
77. 3:11side and the water kind of forms a
78. 3:15horizontal flat line right here okay you
79. 3:18should think that this should not happen
80. 3:20right here this this setup of the fluid
81. 3:23should not happen unless it's clotted
82. 3:25okay so sometimes the entire fluid in
83. 3:28here can actually clot or sometimes you
84. 3:31can see isolated clumps like this okay
85. 3:34the entire fluid the serum does not have
86. 3:37to clot or it to be a positive test
87. 3:39although this is positive it can also be
88. 3:42coagulates positive if you see visible
89. 3:44clumps either one of these cases on the
90. 3:46bottom here would be positive for
91. 3:48presence of coagulase up here if first
92. 3:53of all it doesn't clot at all and if you
93. 3:55kind of turn the tube and it just looks
94. 3:57like normal fluid oh and there are no
95. 4:01isolated visible clumps that would be
96. 4:03negative for coagulase let's go to the
97. 4:05next slide and look at some real
98. 4:07examples okay these are some that are
99. 4:10done in test-tube this one you can see
100. 4:12is pretty clearly coagulase positive
101. 4:15because you turn it on its side and it
102. 4:17looks almost as if it's frozen if you
103. 4:19imagine water and you froze it in a
104. 4:20test-tube it might look something like
105. 4:22this this they turn the test-tube in it
106. 4:24doesn't have any visible clung
107. 4:26and it certainly doesn't look like this
108. 4:28so it's gonna be kalise negative this
109. 4:30does not
110. 4:31these bacteria do not express coagulase
111. 4:33okay
112. 4:34here's another good example of something
113. 4:37that is going to be quite at least
114. 4:38positive right here this is a situation
115. 4:40where it's actually fully clotted and in
116. 4:42fact like we mentioned a lot of times
117. 4:44members of the Staphylococcus genus are
118. 4:47going to be coagulase positive this
119. 4:49specific one which is very common
120. 4:51a very common coagulase positive
121. 4:53pathogen in humans is Staphylococcus
122. 4:55aureus okay
123. 4:56here's two examples right here the
124. 4:58bottom one again you can see you turn it
125. 5:01on its side this one definitely is going
126. 5:04to be coagulase positive again
127. 5:05Staphylococcus aureus but we look at
128. 5:07this one this is an example of a
129. 5:09coagulase negative Staphylococcus
130. 5:12bacteria this is Staphylococcus
131. 5:14epidermidis and as you can see you turn
132. 5:16it on its side and it definitely doesn't
133. 5:19look like this or this so the
134. 5:22Staphylococcus epidermidis is going to
135. 5:24be coagulase negative okay and again
136. 5:27just to reiterate if we had a situation
137. 5:29where we saw visible clumps in the test
138. 5:33tube we would still say it's coagulase
139. 5:35positive okay so hopefully this makes
140. 5:39sense make sure to watch the
141. 5:41demonstration video on the coagulase
142. 5:43test