[MUSIC] Hello, everyone. My name is Lina Cavaco, and I'm here to present you the second lecture of this course. And this course is going to focus on antimicrobials and antimicrobial resistance. So this lecture is also one of the very basic ones to understand what antimicrobial drugs do and how they do what they are supposed to to kill and inhibit bacteria. So we are going to give you some definitions and show you how antimicrobials actually work. So to start with I give you some outline and really we are going to into looking into the bacterial cell. And what are the targets for the drugs, the antimicrobial drugs. Where they have taken their action, how they do that? What are the modes of action? And the modes of action in regards to the spectrum of activity, so in regards to which bacteria they are able to kill and why they do so. So, we are going to define a little bit around bacteria. Don't be afraid. If you don't have the basics of bacteriology, I will guide you through it and we'll look into what happens in the bacterial cell. This is a very busy slide I know, but I'm going to spend some time explaining you. Let's think this is a bacteria. This is a bacteria cell. A bacteria is a prokaryotic organism. So you have a cell membrane, a cell wall structure. You have the DNA in the cytoplasm, there is no nucleus in the prokaryotic cells. And you have all the machinery that the cell needs inside this bacteria cell. And they will divide to procreate, to become daughter cells. They will split into two and they will live their lives happily and maybe some cause some disease one of the days. Many bacteria are not causing disease but antimicrobials are used for the ones that do. So what we are worried about is the ones that are causing disease and are dividing in the human or animal body. And those we want to treat with antimicrobials. As when we give antimicrobials, they have action in some points on this bacterial cell. And one of the main points and starting from the first antimicrobial's discovered which was Penicillin and the drugs related to Penicillin and other groups of drugs. They act on the cell wall. So, they act on the making of the cell wall that when the bacteria divides and cannot make a new cell wall. Then they just are killed because they cannot grow beyond this point. Again when we want to inhibit the growth of bacteria, we can also act on their DNA. So if they are replicating the DNA they are dividing the DNA to make two chromosomes and to split into daughter cells, we can also act there on the DNA replication. And that's what some of the drugs that are used in treatment are doing as well, like Fluoroquinolones and Metronidazole. Then we can also interfere with the cell protein factory. Cells, like every cell, needs protein to make protein to build up their systems. And they will be doing this from the DNA and transcribing the RNA and this can be stopped by some of the drugs that we are using. So some of the antimicrobials would interfere with the protein synthesis either interfering with the RNA polymerase in this case or they interfere with the protein synthesis as well. But then, by inhibiting the ribosomal binding. Also here, that is the ribosomal binding is just that they bind to different targets. Again, in this case, is a very specific target in relation to only gram-negative bacteria, which is a specific group that have this outer cell membrane. You act on this outer cell membrane. Of course it wouldn't work on cells that don't have this one. So, it only works on these gram-negatives. And this is quite important groups as the Polymyxins and Colstin and Amphotericim, and this is kind of an almost mechanical effect as a detergent. This means also that these antimicrobial drugs are rather toxic, but they are actually used in last-case resources when other antimicrobials don't work. That's why we are quite worried nowadays, where resistance to these have been found very very recently. So at the last part, we have metabolism going on inside the cells and for example, one of the important pathways inside the bacteria cell is the production of folic acid. And here you have several substrates going into this metabolism. And several groups of drugs that we are using like Sulfonamides and Trimethroprim, happen to be very alike with one of the intermediate substances. So they mimic one of the substrates, and therefore they stop this process from going on. So in this case, they would interfere with the metabolism inside the cells of one of the essential components. So as you can see, well, there is a number of targets in the bacterial cell, but there's not much more than that. So actually, we are relatively limited. Just to show in another way, we have some of the antimicrobial groups and how they classify in relation to cell wall synthesis, DNA, protein or inhibition of folic acid are here. So there is just in writing in text what more or less the same what I told you in the picture. So, as you can see, there's not so many places where a drug could actually affect. So in a way there is a limited number of targets. This is Is something that limits also the pharmaceutical companies and the researchers there to find new targets,. There is no new targets, they have to invent new drugs that still can act on these targets and get the bacteria killed by that way. So and because I talked about cell wall synthesis and there are differences in the cell walls. If you don't have a background in bacteriology, I must tell you that there are two big groups of bacteria. The gram-positives which have a structure of a cell wall that is quite different of the gram-negative ones. And the basic differences is that while all bacterial have this internal membrane, and then they have this thick layer of Peptidoglycan in the gram-positive cell walls, and they don't have any other structure, any other outer membrane here. So the drugs are able to pass this Peptidoglycan and act on the targets. In relation to the gram-negative cell walls, it is a bit different because there is this outer envelope this outer cell membrane. And then the drugs would need to cross this, which is a little bit more difficult. And they are depending on some pores on this cell wall, and these pores are regulated by some of proteins that are porous. When the drug crosses this, then they would be able to cross this space and act on the targets. So there is some differences, and this makes a difference into which drugs you can use for the gram-positives and which drugs you can use for the gram-negatives. Of course if we use a cell-wall-synthesis-inhibiting antimicrobial which should have a cell wall, there's also some bacteria that just don't have it. So they have a different structure. So in those it would not work at all. And for the drugs that act on the cell wall, there's still some that act on better on gram-positives and better on gram-negatives. So as I mentioned also for the RNA and protein synthesis, there are several places where we can act. While first there would be nucleotides in their genome, and when we replicate the DNA you would have some DNA replication. And when you want to make proteins there would be a RNA polymerase acting. And there would be binding to the ribosome and transcription into protein so that in the end we have protein. If we want to inhibit the cycles, we can inhibit at the basic level. At the DNA level, we can inhibit at the polymerase level, or we can inhibit at the ribosomal level. And that's what happens with these antimicrobial drugs. So we have drugs that act on these several processes. Again, in the DNA synthesis it's rather similar, we also have one molecule of DNA that wants to replicate to two so that we have divided the cell into two cells at some point and there are some enzymes that act on this DNA replication and the structuring of DNA. Essentially for example Topoisomerases that are acting on this super coiling and if you bring in some drugs like the quinolones that act on this specific target the Topoisomerases for example, we have an effect here and the replication doesn't go so well. The cell dies from that so it causes cell death. As I tried to explain a little bit before in the very busy slide, here it is much better explained. This metabolic inhibition of the folic acid synthesis. Folic acid is actually one of the vitamins that we might take as a human, but in the bacteria they produce it themselves, so they need to synthesize it in able to be living, and they have this series of substrates and enzymes that interfere in this metabolism so that they get tetrahydrofolic acid at the end. And here you have these substrates that are very similar to some drugs. So this PABA is very similar to sulphonamide. So they mimic the substrate and stop the synthesis here. And the Trimethroprine is quite similar to this dihydrofolic acid and goes in here. So there would be action in the metabolism itself. So when I talk about different antimicrobials and their different action that also implies that antimicrobials when they get in contact with different bacteria. They might act a little bit different because the bacterial species and the bacterial structure is a little different. So we have some antimicrobials that are quite good. And these are gram positive until, sorry, up to here. And these are gram-negative bacteria. So you have some that act more on one side and some that at more on the other side, and we have also very large spectrum drugs that are able to act on almost every drug. Actually, this should also be grey. Because the Cephalosporins have a very, very broad spectrum as well. We have drugs that are very broad spectrum, and those are the drugs that we use as a choice when we don't know what the infection is, for example. We use the narrow spectrum when we know exactly what we are dealing with and when we want to have a good effect on that narrow spectrum. So, if we think about the spectrum of the drugs, we can have some classifications depending on the classes. The first drugs, the Penicillins, which are still used quite a lot, are more targeted for the gram-positive bacteria. Because some of the gram-positives have been developing some resistance we got some modifications of this drug that were chemically done to target for example more staphylococci and then we had some other modifications that we're to target more the gram-negatives. So they were evolving a long time and new groups of these Penicillins came along. Cephalosporins are also in the same class, in the beta-lactams class as the Penicillins. But they also have evolved from a rather low spectrum and gram-positives only towards a very large spectrum in the third and fourth generation that takes both gram-positive and gram-negative bacteria. Again here carbapenems. These are one of the very last resource antimicrobials. When you get carbapenems in the hospital it's because you are very sick and resistance have arised. And that's where you, you will need to get a treatment with such a drug. Its a very large spectrum and it is used in highly resistant strains also and monobactams are part of this family, also large spectrum. But not exactly as much as the carbapenems but close to. Again, this is for other groups of antimicrobials that target the protein or DNA synthesis. Again, there's differences in the spectrum depending on which drugs you used. The macrolides are more for the gram-positive, tetracyclines are quite broad in spectrum, and fluoroquinelones are quite broad as well, as well as aminoglycocides, Gentamicin for example. And then we have a very specific drug, Metronidazol which is only used for anaerobe, so bacteria that are not breathing oxygen but are living on carbon dioxide sources. So, just to summarize in a very large view of different groups of bacteria, here we have the mycobacteria which includes the tuberculosis agent for example, Mycobacterium tuberculosis and other. This is a very specific group which have different wall structure, so you need very specific drugs in here. So here for example, you will use something like this that is only used for mycobacteria, maybe some of the large spectrum drugs like the amino glycosids have some effect there. The gram-negative bacteria, where you have several groups acting on them. The gram-positive which includes treatment with Penicillins and some of the large spectrum drugs as well. The Chlamydias are also another group that is rather specific which is more dependent. t's not as the defined as other bacteria, it's a little bit different. It is not targeted by many, maybe a little bit Sulphonamides and Tetracyclines, and the Rickettsias which are intercellular bacteria also, are only really affected by Tetracyclines. As you see Tetracyclines actually take up a large group of bacteria, and some of the others take the main groups are these that are causing the main infections. So thank you very much for this lecture. I hope you, you will follow us for the next ones. [MUSIC]
