These are preparations of the same culture that I showed you in the first electron micrograph. Now we're getting real fancy. This is called a scanning electron micrograph. So it's very nice. It's very practical. Oh, you've seen these, by the way in the science magazines of insects. They make movies out of these images, with the big tentacles and everything. That's because you see the outer surfaces in a three dimensional image. That can be useful. But a lot of times when we're studying these microbes, we really want to see inside the cell. So after I've downgraded this form of electron microscopy, it's still yields some pretty and fascinating images. It shows that here is a cross wall and these are the same E. coli cells presented in earlier slides. Now, here is a panel showing what happens after a one hour exposure to amoxicillin at 1, 2.5 or 10 micrograms/ml. Actually, this is like doing titration of how low a concentration you have to go or can be reached while inhibiting the organism. We call that in our field, the minimal inhibitory concentration, commonly abbreviated MIC. It's one of those terms you will come upon, if you ever read anything about antibiotic action, particularly the in vitro activity.

So here you go. Look at the blebs or balloons, there they are right where I said they were going to be. When you go up to this concentration, they're all ready to burst. These are probably all dead cells. I have a similar micrograph with a cephalosporin. This time I identified which one it was, it's Cefaclor, but it could be any of the cephalosporin, producing bacterial cells that form long strands. The cephalosporin didn't produce the morphological difference as a function of antibiotic concentration, as seen with penicillin. There are some blebs there, some here. I did mention that we would eventually see the blebs following exposure to cephalosporin. There are a lot more here in the higher concentration. Again, giving you some titration of the activities of the compound.

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