I've run dr. Mike here now the white blood behind it looks quite busy and that's because there's many different classes of antibiotics and we're going to go through some of those classes we're going to go through some examples we're going to go through how they work and what type of bacteria they kill off so let's have a look now when we go through these I've created my own mnemonic that helps me remember them the mnemonic is antibiotics can protect the Queen's men servants and guards it's pretty dumb but it helps me take the first letter of each one and that's the first letter of an antibiotic class so if we start at the beginning antibiotics the a is going to stand for amino glycosides now this class of antibiotics will kill off gram-negative bacteria specifically watch the video where I outline the differences between gram-positive and gram-negative or one of the major differences is gram-positive bacteria have a very big cell wall surrounding it gram-negative bacteria have a very small cell wall or thin cell wall and they have two membranes as well that's gram negatives are two phospholipid bilayers if the amino glycosides kill off gram-negative specifically two main types or examples of many glycosides are the streptomycin x' and gentamicin x' and the way they kill off bacteria is by inhibiting the protein synthesis so DNA needs to be turned to proteins and proteins do all the function within a cell okay now in order to turn DNA to proteins you need something called ribosomes and every ribosome has two subunits to them for bacteria over 50s subunit and a 30s subunit and the DNA sort of weaves its way in the middle of these two subunits and it spits out and me no acids that fold into proteins now human cells don't have the 50s and 30s subunits we've got a 60s and a 40s subunit so we exploit these differences to kill bacteria off in this case the gentamicin streptomycin stop the 30s subunit from turning DNA into proteins now as we go to the next one we go to can the C stands for cephalosporins they kill off both gram-negative and gram-positive bacteria examples are cefazolin and suffered raxil and again they kill bacteria and he cell wall synthesis so I shouldn't say again we said protein synthesis for the first one cell wall synthesis in this case remember bacteria cells are surrounded by a cell wall human cells are not the cell wall is made up of sugars stacked on top of each other and each sugar is connected by these protein or peptide links and the peptides need to be interlink to one another and so what these particular types antibiotics do is they break the bond between the proteins that hold the sugar molecules together and that way the cell wall just comes apart now this is important because bacteria are hyper osmotic that means they've got a lot of stuff dissolved in the inside of the cell which means the water wants to rush in when water rush in rushes in it wants to burst the cell and the cell wall stops that from happening so if you destroy the cell wall you destroy the bacteria now for the next one p4 protect that's the penicillins you've all heard of penicillins before penicillins are at least the first class of penicillins such as penicillin G only were effective against gram-positive bacteria and that's because it attacked the cell wall again now it inhibits again that cell wall from being synthesized by again breaking those bonds but because it didn't kill off gram-negative we needed a more broad spectrum antibiotic so we started to create ampicillin now the thing is this penicillin G is a very big antibiotic and when you compare gram positive to gram-negative bacteria gram-negative bacteria have two phospholipid bilayers around it okay two membranes one on the inside one on the outside but it's got these pores these little channels to allow things to go past these membranes now penicillin G was too big to get through these pores so it only killed off the gram positive bacteria so what we did was we created ampicillin ampicillin is a smaller version of penicillin G and it was able to jump into these pores and kill off gram-negative bacteria as well okay so the penicillins can kill off gram positive and gram negative depending on the type of penicillin now the other thing is that bacterial cells are really smart and they're very good are becoming antibiotic resistant especially to the penicillins why penicillins work is I told you you've got the sugar molecules of the cell wall stacked on top of each other you got proteins holding them together and then you've got bonds between the proteins they break the bonds between the proteins the way they do this is by the penicillin molecule looks like this okay this square part is what binds up those interlinking portions for the proteins stops them from coming together back T and that's called a beta lactam that's called the beta-lactam ring okay now bacteria have evolved an enzyme now could beat a lactam a's that destroys that ring so stopping peniston's from working okay now we've also got this part called pennis that's the penicillin aspect but bacteria have created penicillin a's as well to destroy that too so what we've done is we've created a new class of penicillin which is called methicillin and methicillin can kill pretty much anything however it's now found out that we've got bacteria that have become resistant to methicillin which is one of the last line of antibiotic defences and they're called methicillin-resistant Staphylococcus aureus M RS a all right let's move on T tetracyclines kill off gram-positive and gram-negative bacteria you've got the tet recycling and doxycycline they do this by inhibiting protein synthesis of the 30s subunit just like we spoke about up here then q we've got the quinolones and fluoroquinolones they kill off gram positive and gram negative as well cipro flaxen is an example of this type of bacteria a antibiotic sorry and in this case we haven't spoken about this yet it inhibits DNA from replicating so in order for a bacteria to stay alive the DNA needs to replicate and create more copies of itself okay but bacterial DNA is wrapped around itself it's this double-stranded circular DNA that's wrapped around itself and in order to make copies of it it needs to unwind and so we need an enzyme that does this unwinding called topoisomerase there's different types 2 and 4 for example and these antibiotics top the top hour summarizes from unwinding the DNA therefore stops it from being able to make more copies therefore stops more bacteria from being made then we've got m4 macrolides they're gram positive specific erythromycin isn't sample may have heard of that one before and it inhibits protein synthesis not the 30s subunit this time but the 50s subunit so DNA can't be made into proteins s4 sulfonamides gram positive and gram negative and this is sulfamethoxazole this is an example and inhibits folate synthesis okay so bacteria can make its own folate for metabolism growth development we cannot we need to get folate from our diet so we can exploit this difference by inhibiting the enzyme that allows us to allows bacteria to make folate it's not going to inhibit us because we don't have that enzyme so inhibiting this enzyme will kill off the bacteria and this is the self on amides then the last one is the glyco peptides this is gram positive specific and vancomycin is an example of this and inhibits cell wall synthesis as well so this is an example of some of the major classes of antibiotics