Drug resistance can arise much faster. There's something on horizontal gene transfer, which is when DNA is passed directly from one organism to another. And that DNA can carry resistance to one or several different antibiotics. The equivalent of this is when you have a baby, you give them your DNA, not directly, but they get your DNA. This is the equivalent of me handing my DNA to Martin and him taking up that DNA. So this is what's horizontal gene transfer is. And this happens fairly commonly in bacteria and there are three ways it can occur. The first way it can occur is something called transformation. And this I'll give you a little historical perspective on this. This was the experiment died in 1928. And what they knew is they had two strains of Staphylococcus pneumonia. One strain is called rough and one strain is called smooth. The rough strain does not cause disease is non-variant. If you inject it into a mouse, the mouse is fine. If you take a smooth strain, inject it into a mouse, it's the mouse dies. If you take that smooth strain and you heat it up and inject it into a mouse, the mouse is fine. So this is a heat-killed smooth strain. But the experiment he did was he took a rough strain with the mouse is fine and the heat-killed smooth strain mixed it together. Both of these alone aren't fine. But if you mix them together, I'm going to have an M house to the mouse dies. And he called this transformation because he could see that the bacteria in this mouse were now smooth bacteria. So what is this magic happening here? It was shown that the transforming principle, the thing that is being transferred is DNA. That was shown in 1944. And what is actually happening here is this. Here, you're back to my boring slides. Here is a cell. And here's a cell. Some cells can take up DNA, either a circles, which we call plasmids, or is linear DNA, just pieces of DNA. And incorporate them either as plasmids, or integrate them into their own chromosome. They can be actively taken up by some types of bacteria like the ones used in the experiment I just showed, or some bacteria do it by mistake. They essentially, they don't mean to do this, but it happens sometimes. Or in the lab, we can induce some bacteria to do this. The cells that take up the DNA, we call confidence. So some bacteria like to do this. Take up DNA. Can you think of why they might like to take up DNA? If you think about, if you think about what DNA is, well, it can be a source of food. They need DNA. They need nucleotides to make more DNA. So it's a nutrition for them. That's one reason. I should say also, nobody for sure knows why, but this is certainly one of them. Other people speculate that it might be used to repair DNA. If you have a break in your DNA, by picking up DNA, you might be able to fix it. And the third way is what you just said is that you can evolve new traits. So if you pick up a gene that is very useful in the future, and it's selected for, that is something that's going to be kept, that you're going to evolve the ability to take up DNA, as well as the new traits. Okay. That's the first way, transformation. Now I want to move into the second way. First I want to talk a little more about placements. So again, placements are small circular DNA molecules. We call them autonomously replicating, meaning they don't have to go into the chromosome. So every time cell divides, it gets placements in copies of placements also. Some placements are many copies, some in only one. Plasements are incredibly common. Most natural strains of bacteria have placements. And they can carry the genes for antibiotic resistance. You might ask where these magic placements come from. Well, they evolve from other types of mobile elements. So there are genes such as, or DNA that, for example, from bacterial viruses and transposons, transposons are helping genes, genes that can help around, as well as bacterial genes. Now I'm talking about placements so much because this is actually the major way in which antibiotic resistance spreads through a mechanism called conjugation. Conegation occurs. It's a currently common. And they can cause genes to spread to unrelated cells. So again, here's our myplasmid with the antibiotic resistance gene. Some placements are called conjugative. Conjugative placements have some extra features. They produce a pillis, I mentioned Pillai last week. A pillis that is this appendage off the cell. They use her conjugation. And this shows an actual picture of two cells where one of them is expressing this pillis and attaching to another cell. So you need the pillis and they attach us to another cell. So let's look at how this happens. Here is the cell that is resistant. We call it the donor. It's producing a pillis. It grabs hold of another cell, the recipient cell. And then the pillis is retracted. And the two cells are brought very close together as shown here. Then what happens is a pore, a small hole between the two cells is formed. And the placements makes enzymes that cause it to cut, one strand of the DNA, and bring it in to the recipient. Shortly after them, both cells have one strand of DNA which is then copied and replicated, ending up with two placements or one placement in each cell. This cell now can go ahead and conjugate with other cells. So both cells now are resistant antibiotics and both can transfer. This in our lab can take place in a couple of minutes. If all you have to do is put the cells together and you don't, it's incredibly fast. And this is the most common way for resistance to spread.