Antibacterial Action
Let's see if that clip can go now. Run that video (unavailable for the web presentation). What this is going to show you is the action of penicillin against an E.coli. I picked the rod shaped organism because once the beta-lactam starts acting on it, it really does--oh, that beehive of activity. This is at low power of the organism in the absence of antibiotic. Lynn was right. You look at them and they're moving all around. They're not particularly interesting in that type of setting. But you can see how fast they're going. If we blew these up to actual size, like our size, these things would be swimming, I don't know, 30 miles, 40 miles an hour. You can't see the flagella that propelling them. They're beyond the resolution of this particular microscopy.
Now we can see at higher magnification. This is out of focus because we're just looking at one plane. These are live cells. Boy, look at them wiggling. Most of them are single cells. This is an untreated population of E. coli. Again, you can't see the flagella. The flagella are peritrichous. That means they're surrounded by flagella, very active. This is a logarithmic phase type of culture (rapidly dividing). But once they're sitting in amoxicillin for about an hour, what happened. Boy, it bombed them. You can see a little bleb forming on that guy. Here is one here. Let's see if I can see these guys while I go in and out of focus. There are some up here. There is one guy here. They form rabbit ears. What's happening is that wall is weakening. It forms a bubble. Eventually, that bubble bursts and kills the cell. That's the very attractive nature of a penicillin or a cephalosporin. Any beta-lactam can destroy the cell, actually kill it. Look at that guy. But see, even though it's bulgy, that god darn guy over there is still swimming. So he's not dead yet. Same over here. He will be. This one is probably gone already. But penicillin is a very, very active killer of cells that are susceptible to it. Cephalosporin, this happens to be an example of one Cephalosporin anyway. What happens here is that it's hitting the crosswall that normally would be there. So what happens, the cell doesn't divide into two equally small cells. It just keeps it as one big long chain. If we did a section through that, you would find that there would be several regions of DNA because that one cell contains several individual cells (nuclear regions) but they don't have their cross walls. Tetracycline doesn't does radically change the cells morphologically. Remember, it inhibits protein synthesis. So the appearance of the cell does not change. Notice, though, the population is dramatically changed. What I did here is that at zero time, I added the penicillin or added the tetracycline, whatever, and another I had as my untreated control. The very first clip you saw was the control after one hour. It grew like crazy. But with tetracycline, although it doesn't change the morphology, the organism was clearly inhibited from multiplying. In fact, some of them, most of them are not moving. Oh, there's Pfizer.
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