We've talked about three kinds or four kinds of resistance. Now, how do they get this resistance? I mean, the biofilm is obvious, but the other types, how do they get this? Well, primarily through or one way is through mutation. So if you have a population of cells, and there's some kind of variation in these cells, when I said that cells divide and they become clones of each other, that's true, but every so often there's a mistake, and there can be some mutations. So there is some variety there. So if you have a population that has a certain amount of variety or genetic variation, and you add a selection, for example, in antibiotic. After the selection, the only guys that are left are the most resistant. Those are resistant ones, then can grow up and take over the population. So that's a simple idea of evolution and selection. So mutants can arise from the original mutants and the genetic variation can arise from damage to DNA or mistakes during DNA replication. I'm going to show you DNA one more time. Here is DNA again with the base pairs, of course, where it is always supposed to match C with G and A with T. As I mentioned before, here's the DNA, here's the RNA, and then each of these codons, so AUG becomes methionic. If you make a change in any of these bases, you will change the protein, as shown here, if we look up. Here is a simple example where everything is C, I, T, C, I, T, C, I, T, which should be his, his, his, his, his, his, histidine. If you change one of these bases to from an A to a C, all of a sudden, when the ribosome makes this protein, you have his, his, his, and their pearly. These could completely change the protein and it could make it completely inactive. So mutations are in the DNA, but then they're usually expressed in proteins by changes to the protein. So this can happen during replication, but it can also happen by chemicals or UV damage. So ultraviolet light can attack DNA and form dimers in the wrong direction here, between two T's in this example. So thymine dimers. This is why UV damages danger is the bacteria and the people. When the cell goes to replicate this, it's got this big mess here, and often it doesn't quite know what to do with it. So it will make mistakes in replicating this DNA. There are repair enzymes that try to fix it, but again, they can make mistakes as well. So that's how you get this variation, that how you get mutations. So a single base change can cause resistance to some antibiotics. These mutations are rather rare. It's far as for DNA replication on the order one in 10 days, seventh or one in 10 days, nine cells. But there are many, many cells. One of those little colonies has like 10 to 7 cells. So when you have such big numbers, this small number isn't so small.