[MUSIC] Hello everyone. My name is Lina Cavaco, and I'm here to present you the third lecture of this course. And now we are getting into the fun stuff because we have been giving you some definitions on what antimicrobials and antibiotics are, and we have been looking at the classification and the targets, how they act. But now we are going to tell you more about how the bacteria actually are very smart and they get ahead of antibiotics and become resistant to them so that they actually don't work on them. So in this lecture, we are going to define what is resistance and what bacteria that are resistant are in general. What bacteria do to become resistant. So what are the basic types of resistance? What are the mechanisms they use? And we are going to give some definitions about antimicrobial resistance in this subject. That is a very broad subject that many researchers are working on. We are going to define a little bit what intrinsic resistance is, so the resistance that is natural, and what is the resistance that is acquired, so the one that the bacteria can get from other. And co and cross resistance which are kind of some terms that we need to know to know a little bit how it spreads. And we are going to give some examples, and look at an overview of how resistance can arise. So to start with, we need a basic definition. So how does a bacteria become resistant? Either they acquire something, or they are spontaneously become a resistance. Is it that way. Well if we think about acquired resistance, the bacteria are becoming resistant by getting something and they get something that is a change. And this change, well it is in their genomes. So, if they acquire a mutation in a part of their genomes, a spontaneous mutation that can occur, they might become resistant. And it is a endogenous resistance. It's their own chromosome that is modified and therefore they can transmit it to their daughter cells, but they cannot really share it around. But then they can also acquire a change that comes from the outside. They can acquire a new piece of DNA, a new piece of information that will act on their own cell. And they actually can be transmitted to other cells, so they can be transmitted horizontally to others. It is a little bit maybe a difficult concept to think that parts of the genome can be shared. But actually, this happens in the nature quite a lot. And it can happen in several ways. The gene transfer, so parts of DNA, parts of the genome, can be transformed, since we have maybe some DNA, pure DNA that is in the environment that could be acquired by some bacteria that are competent which means that they can acquire this DNA and put it into their own. Then it can happen by transduction, and this happens when these funny looking viruses and these are viruses that are called bacteria phage's because they eat bacteria. Well they don't eat them as such, but they infect bacteria, and by infecting bacteria they will have this structure that attaches to bacteria, and they can actually inject some DNA into the bacteria, and they can acquire some DNA from the bacteria and transmit it to others. So in that is called trandsuction by phagis, by bacteria phagis, where the DNA from one bacteria can be transducted to another one. And then there's another phenomena, that is conjugation. And that happens between bacterial cells. So one bacterial cell. For example, take this one. That has its own chromosome and that has the circular DNA molecule that is a plasmid. This is a circular DNA that is a multi-replicated self. And that is the additional part of DNA that includes some information that is extra for these bacteria. Maybe this bacteria has it, because it needs it. And then another bacteria that does not have it might want to have that part of the DNA, because it was confer them some advantage, like antimicrobial resistance. And the conjugation would be these cells getting together. It's a species of sex between bacteria where is created from one bacteria from another, and this DNA would be transferred to the other. So this bacteria that has no plasmid, will then have this plasmid, because it will get it from the other. So this happens between bacteria of the same species, but sometimes even of different species. So in this way, any resistance genes, or any genes that are in these plasmids, can easily spread and transfer to many bacteria. So that's why we are quite worried about this horizontal transfer of resistance. And then we have inside this acquired resistances we have different ones. We can have for example intra-cell accumulation of the drug. Because the drug doesn't come into the cell or because we have some pumps that make it pump out of the cell. So in this case, the resistance arrises either because the drug is really not able to reach the cell or. Is so fast the pumped out that it doesn't have time to do the effect. Then we can also have a very basic type of resistant that is acquired where we have a gene that encodes an enzyme. And these enzymes are able to inactivate the drug so that the drug is broken down and it doesn't have an effect anymore. As part of the acquired resistance we can have some mutations as well where the target of the drugs so we've spoken the last lecture about the different targets where the drugs could acts, then there would be specific targets. If this targets is looks different now, because it has been modified by this mutation. Then it will be different, and then the drug cannot act on it. So by mutation or chemical modification maybe the target is not available or changed in a way that it doesn't work anymore, or it could be some proteins that actually sit around the target and protect it so that the drug doesn't get in contact with it. Or there could be some over expression of another target. So instead of the bacteria having the real target then it has a fake one or a new one where it is trapping the drug so that the drug doesn't have an effect. So we have several mechanisms here that are quite basic in resistance, and they are used by many bacteria to get resistant. But we have a concept that we need to take straight. Some species of bacteria are actually naturally resistant. So if we consider resistance as a phenomenon that is acquired and becoming worse and worse and we see it in the news, we also have some species that have always been resistant to something. So it is because the spectrum of the drugs is different, so some bacteria are just not possible to kill with that drug. And this is a tolerance by a group of bacteria, which could be a species. It could be a genus. And it means that the drug is either not accessible for that bacteria, that it doesn't get in, or it just doesn't make the way to the target, or that the drug is expelled by the bacteria, so in some ways, the bacterial species or group is really not affected by that bacteria. And we know some of them, so we are not testing as such for them because we know they exist for certain species in combination with certain drugs. But then also in the same intrinsic resistance, some bacteria also produce some enzymes which they always do. It is enzymes that are encoded in their own chromosome and it's not a new thing that is come in, but it's because these species have these enzyme production. So, this actually also inhibits some drugs. And it could also be a kind of lack of affinity for the target because they have different targets and it could be because they just don't have the target. As I mentioned in the last lecture about the cell wall, some bacteria just don't have a cell wall that looks like that. So they would never be effected by drugs that affect this kind of cell walls. So, but when we speak about resistance in general, we have the intrinsic, we have the acquired, and we also have some factors that affect the levels. Resistance is not always black and white, it's not all or nothing. And we can also have some natural levels, of resistance of the species, which makes it higher or lower. For some species, even though it might be not intrinsically resistant, but it could be a little higher. It could be having a resistant gene or a mutation involved. It could be that the gene in question is not expressed In the same way, in the same strain or in the same species. And it could be because there is just other genes as well that play together with the ones that are causing resistance, so that the levels are different. So an example of the natural level of resistance, for example, is if we have Species 1 and Species 2. If we measure resistance, and we do this by testing the minimum inhibitory concentration, and the higher the minimum inhibitory concentration, the more resistance it is. Well, if you try to guess, then species two seems to be much more resistance than species one, right? But this is just a normal species one and a normal species two. So actually they are not specially resistant but they are just normally like that already. So the level of resistance, the natural one is different. Another concept is also a basic definition is cross resistance. And that means that two drugs that are relatively similar that are related can actually have resistance in one species or in a group of bacteria. Just because one mechanism is present, so the bacteria has one mechanism of resistance, but it effects all the drugs that are similar. So in a way the bacteria is producing one enzyme or is having one mechanism, but all the drugs that have some relation, they would be not working on this strain. So that is cross-resistance, which is a little bit different from the next concept that I will explain which is co-resistant. And here the thing is, well the bacteria Is the same bacteria. But they are harboring maybe resistance mechanisms. And here, they would be maybe some, several different mechanisms. Which are in the same genetic element, so they are together in the same genetic structure. But then they are able to cause resistance to drugs that could be different. They could be similar in the same families, but they could also be very different classes of drugs. And the example that I have here is a real example this is from a interococci which are a grand positive cocci. And some of them have this plasmid. And this plasmid causes vancomyze in resistance because they have this resistant gene towards vancomyzin. It causes urethral niacin resistance, which is another class. It's a microlide, and still it has another resistant gene that causes resistance to something different. It causes resistance to copper, which is a metal. So every time this plasmid is transferred to a new internal It will become resistant to all these three different classes. It's not because vancomycin is very related to, makrelites or to copper, it's just because it just goes together. So here is just an overview. It is busy, but I'm going to get over the main structures and it is to summarize some of the mechanisms. So if we have a drug that is outside the cell and trying to get in one of the mechanisms is to interact here with the permeability. So to affect the way the drug will be able to get in or not letting it get in at all. The B would be an alteration in the replication or the replacement of the target, so if this drug should act with this target if you change the target so that it looks different it cannot really bind. In regards to the C, if we have a drug and there is an enzyme modifying this drug so that it becomes different then this drug might be destroyed and not active anymore. Another very big mechanism that is many times causing multi drug resistance, is that, well the drug is able to get in but then there is a pump that is pumping it out, so it's not effecting inside the cell anymore. So to summarize some of the applications of this mechanisms. A really large number of genes, and here we are talking about hundreds and maybe thousands of genes cause this inactivation of the drugs. So when we talk about beta-lactamases and other enzymes, then we are really talking about enzymes that are produced that modify or destroy the drugs and that affects several classes of antimicrobials. When we talk about the target or the target modification, then we might be talking about tetracycline and floroquinolones where the target can be affected so that the drugs don't work. We have a very concrete example like mecA and mecC which is not on the slide but should also. It's a similar agent where this new target is made so that the drug would try to act on the fake target and not on the real one. And then would be some drug trapping or titration, which is by hyperproducing Than the target, that does also affect other classes of antimicrobials. So these are some examples of how the bacteria are very smart, and are able to target and to manage drugs when they come in. This is a very busy slide, I know, again, but if you take it from the bacterial perspective, we have the outer membrane so this outside of the bacteria. This is the space between the outer membrane and the cell wall. The inner membrane and what happens inside the cell. So if we start inside the cell, well there's many many things going on. The DNA is being replicated. The protein is being synthesized, and sub-metabolism is happening, so we have different drugs acting on this. So this is RNA polymerase changes, this is on the DNA replication that we have other classes acting, and on the metabolization, we have other classes acting, and also in reduction, modifying enzymes that also act here. They could be acting here causing resistance. And here also in the protein centers. So, this is all going inside the cells. Different classes of antimicrobials doing different things. Here on this space, these are mostly the targets. Of the penicillin and beta-lactamases that are penicillin binding proteins. So these drugs would be trying to act on the penicillin binding proteins and there would be some beta-lactamases that are causing resistance to some of these drugs. Which are enzyme that just breakdown the drugs and that could be also some ligases that are quiet, some genes that are changing to use drugs here now. And outside of the cell what happens normally is that it doesn't let the drug in or that it pumps it out. So here we are talking mostly about permeability and porin deficiency, which can effect also many of these drug groups or these pumps. Many times these pumps cause multi-drug resistance because they are not only pumping one type of drug they can pump several ones. Sometimes they are more specific. So it is effecting a large number of drugs. So in a way the bacteria finds solutions and finds solutions to defend itself against antimicrobials. Because of course these are weapons made to kill bacteria. So the bacteria are very smart and get their own ways to get rid of them. And that's what is interesting about, and we are going to talk more about in the next lecture, where we go into resistance and testing resistance as well, yes. Thank you very much. And I hope you are on for the next lectures. [MUSIC]
