Microbiology: Hemolysis/Blood Agar — Transcript

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1. 0:00My name is Kevin Tokoff, and in this
2. 0:01video, we're going to discuss the basics
3. 0:03and theory behind the hemolysis test and
4. 0:06blood agar.
5. 0:07Okay. So, some organisms such as those
6. 0:10belonging to the genus Streptococcus
7. 0:12are what we call fastidious organisms.
8. 0:15And that's because they have special
9. 0:17nutrition requirements, and not every
10. 0:20type of agar is going to be able to
11. 0:22facilitate their growth.
12. 0:24And so organisms such as Streptococcus
13. 0:26might need to be grown on enriched
14. 0:28all-purpose media.
15. 0:30Um one example of an all-purpose agar
16. 0:32base that we can use is trypticase soy.
17. 0:36Um we can also enrich that agar with
18. 0:40uh red blood cells. And this is usually
19. 0:42done by using some percentage of
20. 0:46red blood cells from some organism. For
21. 0:47example, we're going to make something
22. 0:49called blood agar, or we're at least
23. 0:51going to use it. And our blood agar is
24. 0:53going to contain 5% sheep blood, and
25. 0:56that's going to specifically contain the
26. 0:57red blood cells.
27. 0:59Now, hemolysis. Hemolysis is the process
28. 1:03of destroying red blood cells by some
29. 1:06mechanism. Okay? If you ever see the
30. 1:07term erythrocyte, that also means red
31. 1:10blood cell.
32. 1:11Okay? So, the hemolysis test tests a
33. 1:12bacteria's
34. 1:14ability to destroy red blood cells.
35. 1:16And some bacteria, uh which would be
36. 1:19positive for hemolysis, um are going to
37. 1:22make enzymes called hemolysins. And
38. 1:25these are enzymes that destroy red blood
39. 1:27cells. Um if you've ever heard of the
40. 1:29term hemolytic anemia, that's an anemia
41. 1:32where we have destruction of red blood
42. 1:34cells. Hemolytic hemolysis. Okay?
43. 1:37Destruction of red blood cells.
44. 1:39Now,
45. 1:41different species contain different
46. 1:43classes of hemolysin. Um some contain a
47. 1:46beta hemolysin, others contain an alpha
48. 1:48hemolysin. This gamma is a little bit
49. 1:50misleading. The gamma basically means
50. 1:52they don't express hemolysin at all.
51. 1:55Okay? In which case there's going to be
52. 1:56no hemolysis.
53. 1:58Um for bacteria that beta and alpha
54. 2:01hemolysins, um, they're going to destroy
55. 2:04red blood cells, but the patterns that
56. 2:05you're going to see on the blood agar
57. 2:07are going to look a little bit
58. 2:08different.
59. 2:10Okay? And so we're going to look at
60. 2:11those patterns on the next slide and
61. 2:13sort of discuss what they mean. Okay?
62. 2:17So these are the results of hemolysis
63. 2:19tests. Okay. So I've got here presence
64. 2:22of some type of hemolysin produces and
65. 2:25we're going to look at what the pattern
66. 2:26is. Okay. So if we have what's called
67. 2:30beta
68. 2:31hemolysis, so let's look over here first
69. 2:33where I have this beta. Now the actual
70. 2:36where at my mouse is the kind of um
71. 2:39tan region right here that actually is
72. 2:41the beta right here. That's actually the
73. 2:43bacterial smear. That's where they
74. 2:45smeared the bacteria. Okay?
75. 2:48So when you have beta hemolysis, you
76. 2:50have complete hemolysis of the red blood
77. 2:53cells around the smear, um, and you have
78. 2:56transparency.
79. 2:57So what happens is is because blood agar
80. 3:01contains red blood cells, it's very
81. 3:03turbid. So to see the patterns a lot of
82. 3:05times you have to hold it up to a light.
83. 3:07So you can either hold up if there's a
84. 3:08light on your on your lab bench or on a
85. 3:10to a ceiling light. And this sort of
86. 3:13yellow-looking region that's surrounding
87. 3:15the beta and also it's here in the
88. 3:17center um of the beta, that's the zone
89. 3:20of transparency. Okay? And you'd be able
90. 3:22to see that it's much easier to see um
91. 3:24when you're holding it up to a light in
92. 3:26the lab. You'll kind of get the hang of
93. 3:27that. Here's another look at beta
94. 3:29hemolysis. Um, you can definitely see um
95. 3:32it's definitely the brightest when you
96. 3:34hold it up to a light. Um, and that's
97. 3:36how you recognize beta hemolysis. Okay?
98. 3:39If we have alpha hemolysis,
99. 3:42um, there will be a zone of change
100. 3:45around the bacteria, okay, around the
101. 3:48colonies, but
102. 3:50um we don't have transparency. Okay? So
103. 3:53if you look at this, this is alpha
104. 3:54hemolysis. So you can see the dark
105. 3:56regions right here. That's kind of where
106. 3:58the bacteria were smeared.
107. 4:00And we see a little bit of
108. 4:02around that, but it's definitely not
109. 4:05transparent. And again, it's much easier
110. 4:07to see whenever we hold it up to a light
111. 4:09in the actual lab. Okay?
112. 4:12If we have gamma hemolysis, this is kind
113. 4:14of a misleading term. Gamma hemolysis
114. 4:17basically means there's no hemolysis.
115. 4:20There's no destruction of red blood
116. 4:22cells. And so this is sort of what we're
117. 4:24seeing for gamma hemolysis. All we see
118. 4:26is the streak of bacteria, the colonies,
119. 4:29that's all we see, and there's no
120. 4:31destruction of red blood cells here.
121. 4:33Okay? And we can either record this as
122. 4:36gamma hemolysis. I think in your lab
123. 4:38manual here, it actually wants you to
124. 4:40record it as non-hemolysis. Just
125. 4:42understand this is also in some schools
126. 4:45of thought called gamma hemolysis. Okay?
127. 4:49So hopefully this makes sense. Um make
128. 4:51sure to watch the demonstration video on
129. 4:53the hemolysis test.