Let's see where am I in this program? Okay, I'm going to go on with the slides. One of my favorites. This, this is a difficult slide to read, so I'll read it to you. This is a plate containing blood agar. This is just agar with sheep red blood cells put in it. This is blood agar with sheep red blood cells put in it, but here we've streaked Streptococcus pyogenes on it.

How many have had strep throat in their life, how many people in this audience? When I go to schools, if you ask your students, 90% are going to raise their hand. That's why this is a nice topic. This is where the area of microbiology gets personalized. It's not far removed in some distant textbook, but relates to an experience most of the students have experienced. The creatures that we're going to talk about and have been talking about are part of you; most don't make you ill. Most patients have experienced having their throat swabbed to obtain a sample for analysis. After the doctor or nurse takes the sample, they streak it on a blood agar plate, such as I showed in the slide. After streaking the sample on the agar surface, they usually put a little disk over here, a Bacitracin disk. You can see now the difference between this plate and that plate. Can you see any difference there other than growth? Do you have any idea of what's going on in the immediate vicinity of the growth? Lysis, that's right. Lysis right here. The organism is lysing the red blood cells so they're clearing it up. The red blood cells usually produce an opaqueness to the agar; after lysis, the agar almost becomes translucent. The presence of a pinpoint colony that giving you hemolysis (red blood cell lysis) is a good indicator of Streptococcus pyogenes. Now what about that Bacitracin disk? What's happening around the disk? Any clues on that one? Inhibition, right? Inhibition of the growth. By the way, this is inquiry based teaching. Did I get it right? Now you've got two things going. You have a blood agar plate with these pinpoint colonies that are lysing the red blood cells, giving those clear zones and the growth is inhibited by Bacitracin. These results provide a very, very high indication that you have a group A Streptococcus which is Streptococcus pyogenes, the strep throat organism.

In the exhibit we have a station that includes information about flesh eating bacteria. It says, if you look at it closely, that the flesh eating bacterium is a group A, Streptococcus. That's exactly right. It's the same creature that I've described here, but it's one that produces a lot of enzyme, maybe something like hyaluronidase, which degrades the cement that holds tissue together, or rather the cells of tissue together. When it does that, it then causes necrosis. That's the flesh eating part. Now, in order to control that, you have to actually cut that portion out because the blood supply can't get into it. Therefore, if you take an antibiotic, you can't effectively treat the infection because the blood containing the antibiotic can't get to the tissue. Otherwise, the organism is quite susceptible to normal agents such as penicillin.

Narrative Index

Table of Contents

BioForum Index

AE Partners Collection Index

Activities Exchange Index