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Learn the toughest concepts covered in Microbiology with step-by-step video tutorials and practice problems by world-class tutors.

10. Dynamics of Microbial Growth

Differential Media


Differential Media

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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 played cells on differential media you'll be able to distinguish them visually. And so the most common example of differential media are blood auger 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 Hamal Asus. And hm analysis is simply the lice ist 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 Hm analysis or bacteria that perform health. Alpha Hm analysis are going to generate colonies that are surrounded by a small greenish zone of clearing formed by what's known as partial Hamal icis of the red blood cells. And beta analysis is going to be forming colonies that are surrounded by a very large zone of clearing from complete Hm analysis rather than partial hm analysis. And so if we take a look at this image down below, we can get a better understanding of how these blood auger 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 played it all over the surface of this plate. And then what we can do is we can play different types of hemolytic bacteria. Non hemolytic bacteria do not lice 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 uh non hemolytic bacteria that is being plated here. Then up here, what we have is alpha Hugh melodic bacteria. An alpha hemolytic bacteria. They produce a relatively small greenish zone of clearing from partial Hamal Asus. 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 Hamal Asus. Uh And so what you can see here in this image is this whole border right here is the large zone of clearing. And uh the beta hemolytic bacteria are the ones that are plated here street right here. And so ultimately these differential, this differential media uh specifically the blood auger plate allows us to visually be able to differentiate these three groups of bacteria. Um once again, the non hemolytic bacteria have no zone of clearing. The alpha hemolytic bacteria have a small greenish zone of clearing from partial Hamal Asus, and the beta hemolytic bacteria have a large zone of clearing formed by complete Hamal Asus. And so this year concludes our brief lesson on differential media and blood auger 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.

A blood agar plate is a common type of differential media. If there are different species of bacteria on a blood agar plate, what will the zones of clearance around the bacteria show you?


Streptococcus pneumoniae is an alpha-hemolytic bacterial species. If Streptococcus pneumoniae is grown on a blood agar plate, what characteristics will the zone of clearance for this species have?