In this video, we're going to begin our lesson on differential media. And so differential media is going to be a specific type of microbial growth media that contains an indicator that allows for microbes to be visually distinguished by chemical differences. And so when you plate cells on differential media, you'll be able to distinguish them visually. And so the most common example of differential media are blood agar plates. And these blood agar plates can identify different types of hemolytic microbes. And hemolytic microbes have the ability to cause what's known as hemolysis. And hemolysis is simply the lysis of a red blood cell. Now hemolytic microbes cause a clear area around the colony forming what's known as a zone of clearance. And the zone of clearance is really important for identifying different types of microbes. For example, the zone of clearance has a different appearance for the different types of hemolytic bacteria. Alpha hemolysis or bacteria that perform alpha hemolysis are going to generate colonies that are surrounded by a small greenish zone of clearing, formed by what's known as partial hemolysis of the red blood cells. And beta hemolysis is going to be forming colonies that are surrounded by a very large zone of clearing from complete hemolysis rather than partial hemolysis.
And so if we take a look at this image down below, we can get a better understanding of how these blood agar plates serve as differential media. And so on this plate here, the red that you see, represents the blood agar plate, and there's actually red blood cells plated all over the surface of this plate. And then what we can do is we can plate different types of hemolytic bacteria. Non hemolytic bacteria do not lyse the red blood cells. And so notice that, over here, this is the non hemolytic bacteria, and there is no zone of clearance around this, non hemolytic bacteria that is being plated here. Then, up here what we have is alpha hemolytic bacteria. And alpha hemolytic bacteria, they produce a relatively small greenish zone of clearing from partial hemolysis. So notice that there is this greenish clearing that is relatively small that is surrounding these alpha hemolytic bacteria that are plated here. And that greenish clearing is basically the background that you see right here. And then last but not least over here, we're showing you the beta hemolytic bacteria. And the beta hemolytic bacteria, they are going to produce a very large zone of clearing from complete hemolysis. And so what you can see here in this image is this whole border right here is the large, zone of clearing. And, the beta hemolytic bacteria are the ones that are plated here, streaked right here.
And so, ultimately, these differential media, specifically the blood agar plate, allows us to visually be able to differentiate these three groups of bacteria. Once again, the non hemolytic bacteria have no zone of clearing. The alpha hemolytic bacteria have a small greenish zone of clearing from partial hemolysis. And the beta hemolytic bacteria have a large zone of clearing, formed by complete hemolysis. And so this here concludes our brief lesson on differential media and blood agar plates, and we'll be able to get some practice applying these concepts as we move forward. So I'll see you all in our next video.
