Today we're going to talk about antibiotics. So we refer to these as antimicrobial drugs. We're going to focus on the kinds of antimicrobial drugs that kill bacteria, but there are other classes that your book does cover. Antibiotics revolutionized medicine. There's just no other way to say it.
A hundred years ago, dying of infectious disease was extremely common. And some data for you, one out of every three children died of an infectious disease. infectious disease before the age of five. So when you look at how our life expectancy as humans has gone up a tremendous amount over these years, a lot of it is due to the fact that people don't die young of infectious disease nearly as frequently. Now, of course, this is dependent on where you live.
So in poorer countries, you still have very high death rates from infections. And in fact, you can give... people in those areas a couple doses of antibiotics. They've done some studies and they've shown that that cuts the death rate of infants by as much as 25 percent.
What does this mean? It means that infectious disease is so prevalent that if you just reduce some of it, you actually can reduce the death rate. It's kind of amazing. We are going to say that it's the wrong thing to do to just give people antibiotics prophylactically.
They're a valuable drug. where they're losing their ability to be effective, which is what we're going to talk about in our next lecture. And so it's not good to just give people antibiotics to prevent infection. But these are places in the world where infectious disease is a tremendous problem still. So antibiotics are small molecules.
They're produced by, at least some of the first ones that were discovered, are produced by organisms that live around antibiotics. around bacteria like molds, penicillium, cephalosporium. You know, they don't want the bacteria to cause an infection in them. And so they produce these molecules. There's basically chemical warfare that these molecules are produced to kill the bacteria, to protect the molds.
Bacteria that typically live in soil, the organisms in the group Actinomycetes, they also... will make antibiotics. And of course they're just trying to kill other bacteria. So it's literally germ warfare, except for it's the germs having a war with other, excuse me, with other germs. This picture here shows a agar plate, a nutrient agar plate.
And you can see that someone has streaked Staphylococcus aureus on the plate. And then there's a little piece of mold here at the bottom. And you can see that where the mold is around it, we have a ring of no growth.
the staph. So the antibiotic that is being produced by the staph is inhibiting the growth of the staph aureus. And this is exactly what the mold wants to do, right? It's keeping the bacteria at a safe distance so that the bacteria doesn't go in and try to use the mold as a food source.
One of the things we think about when we think about antibiotics is that they have selective toxicity. If you had an infection, I could cure your infection by you know, putting you in an autoclave, but it would kill you too, right? So that's no good. That's a terrible method for treating a bacterial infection.
What you need are molecules that kill the bacteria, but don't hurt the host, that don't hurt you. And so what makes antibiotics really special is they have little or no toxic effect on the animal taking the drug, but they are effective at killing the pathogen. How does this work? Well, it...
It takes advantages of differences between our cells and bacteria. So your cells are eukaryotic. They have a nucleus.
They have these other organelles. Your mitochondria, the energy production of the cell happens in the mitochondria, separate from the cytoplasm and the plasma membrane. So you have 80S ribosomes instead of 70S ribosomes.
There are enough differences that we can find these differences. We call these targets. And we try to...
design drugs that will hurt the bacteria but not have an effect on the person who's infected. And this has been referred to as a magic bullet. So this is Professor Ehrlich. He was one of the first scientists to really try to find specific drugs to kill bacteria.
And he made a drug called salversan that contained silver that was effective, although fairly toxic, at killing the the organism that causes syphilis. So for a while that was the only option for syphilis. There was a myth about a magic bullet, this idea that you could, you know, shoot a bullet and it would curve around. the good guys and only kill the bad guys. And so we refer to antibiotics often as a magic bullet because you can take them orally and get them in your body and they leave your cells alone, but they target and kill the bacterial cells.
And then I was talking about this one semester and a student sent me this video. All right, that kind of shows the example of the magic bullet. The person who first discovered, we call, sort of think of him as the very first person to discover an actual antibiotic was Alexander Fleming.
And he discovered penicillin in 1928 and he did it by accident. He was growing bacteria in his lab. Apparently he was kind of a slob, not a particularly tidy guy, and he went away on a vacation. And when he came back, he had mold growing on his plates. And around the mold, the bacteria had not grown while there were staphylococcus on the plate.
And I think he was planning to throw the plate away. And his assistant encouraged him to try to figure out, you know, what was keeping the bacteria from growing. And so he investigated further and discovered that this was a penicillium mold.
That's the name of the mold. And we call the molecule that it produces that kills bacteria penicillin. From 1928 to 1940, this went from an interesting academic discovery to two scientists named Flory and Chain performing clinical trials. And then in 1945, all three of these individuals won the Nobel Prize in Medicine. Now, if you think back on world history for a moment, I know this is a biology class, but 1940 to 1945 was a big period of time for the United States, in fact, for the whole world, because that's the span of World War II, at least the part where the U.S. was involved.
And in World War I, more people died, more soldiers died of infectious disease than died of their battle wounds. So they might get hurt, but it would be the infection that killed them, not the actual wound. So what changed in World War II is that we had penicillin. And one of the reasons penicillin production ramped up so quickly and became so widespread is that it was so desperately needed to treat.
soldiers that were injured in war. So it was an important application for antibiotics this World War II. And of course, it was a time when manufacturing of everything that was needed for the war effort was supported and funded by the government. And so it made this particular process happen really fast. So we went from this sort of pre-antibiotic era to a fully antibiotic era in just a few years because of the timing of this discovery.
All right, so this is just a little bit more of the timeline. There's another drug called the sulfonamides, and so we're in the class of drugs called the sulfonamides. And these are actually discovered in a lab. So these are synthetic molecules as opposed to penicillin, which is a natural product of a penicillium mold.
And so between these discoveries and then World War II, by the time the 1950s rolled around, there were several antibiotics in clinical use. So this is a little bit of the background, the history of antibiotics. Okay, so I'm going to show you a short video.
It's a bit of a cautionary tale in terms of introducing new drugs or new formulations of drugs. And then I'm going to go on to talk about broad categories of antibiotics.