I'm dr. Becks and I'm going to run you through the inquired practical for microbiology which is found its way into the triple science biology specification and the interesting thing about this practical is it is probably the first time either you or your teachers have worked with a real-life bacterial culture which is what we've got in there it's actually a coli but it's a strain of e.coli that does not cause sickness so it's a very safe strain of e.coli but nevertheless we have to do everything as though we were handling a dangerous micro so the first thing you would have done before you got this far would have been to set up your equipment and you would have washed your hands very thoroughly and you would have removed your work mat from the sterilizing solution in which your teacher would have placed it before we start even handling the microbe we're going to get the agar plates ready now you've probably worked with these before in school but the most important thing is is that you do not open the lid unless you really have to and when you open the lid you're going to open the lid near your Bunsen burner your Bunsen burner is what is going to create a sterile area here where the square is on your workstation and everything you're going to do is going to be within that sterile area so do not pick it up by the lid do not pick it up by the base it's the first thing we're going to do is we're going to mark the agar plate into three sections now if you ever handled one of these before you will have automatically labeled at the bottom not the lid it's the bit where the gel is that you want to have labeled and you're going to put a spot into the center of each triangle because we're going to be using that later and now because we are actually going to be working with the real bacteria we're going to make sure that we've written on the side so that it can be clearly seen by anybody that we're working with you coli you're also going to write today's date on it in case this plate is left in the fridge or in the incubator and somebody wants to know how old it is because it is important that people know what is growing on these plates and then you're going to put your initials so yours can be found again among the whole classes work when you need them later and now you can put your plate down lid up you might have heard before that you should always store them upside down we're not actually going to store that plate for very long we're going to leave that plate lid up for now because we're going to be working on it and we want to place it into our area okay so what we're going to do next is we're going to inoculate the plate now this sheet has been disinfected that's fine but say I'd handled something in them in the meantime so I've gone to write on my notes or even just leant on the rest of the desk or any area that you haven't disinfected then you've got to go and wash your hands you just make sure that you are not contaminating your culture there's actually a greater risk of you contaminating the culture here than this doing you any harm whatsoever it's all about keeping this sterile so to create that lovely sterile environment we're going to turn the Bunsen burner to blue flame now you have never been allowed to be anywhere near that blue flame you've always been warned that that is a dangerous flame this is now creating a sterile environment that we need so this bottle contains a small sample of the bacteria that we're going to grow and we need to get this out of here onto there without any contamination and this is where you have to pass a very strong little finger so what we're going to do this is sterile this is a sterile pipette sterilized by being wrapped in normal crisp red paper and just heat it in an oven it's sterile inside and out it's the inside of it that matters to me not the outside so I can handle it in order to put the bulb on the end of it but I do not want to handle the pointy end I went to handle m10 and I was quite careful well turning it to make sure that I'm going to remove it by the blunt end to star all inside and it's sterile on the outside except with my fingers are now the course I've washed my hands put the bulb over it and now this is clever bit you're now going to hold that with your thumb and your first finger so you can use it because you need this hands to hold the bottle and this hand throw up at the bottle so the first thing you do is you loosen the bottle using your little finger holding onto the bottle you could start to loosen it before you pick it up with both hands if it was stiff you have a problem there turn the bottle not the lid and you are going to flame the lid you are not going to play with a pet so flame the lid gently through the Bunsen burner and now the lid is sterile and you're going to take up about one mil it's probably about it of the solution it's in a sterile pipette it's a sterile solution except for the e.coli I might want to use this bottle again so I'm going to flame the lid again and I'm gonna put the lid on without burning my hand when you do this yourself it's your hand now I've got my agar plate the right way up so this is the lid I'm going to open the lid to the minimum amount of time and squirt my culture of bacteria onto the plate minimum opening minimum time squirt close and now like the pet goes into my discard bottle so at the moment my bacterial culture is just lying in the middle of my plate so I need to spread it so your lovely lab technicians have been working in the background to prepare this for it will out wrap the glass shredder in grease group paper and it's been in the oven so I'm only gonna hold it on this end batter and is sterile don't want to go anywhere near that end at all and I want to use this spreader to spread that liquid out over the entire agar plate so blue flame lid off pointed towards the plane with as little time open as possible spread the bacteria over every single part of the plate and this is one of those little jobs where if you don't do it correctly we will know because the bacteria won't grow right to the very edges so there we are and close the other thing that we're going to know straight into the discard bottle and I like the Burk onto that now the other thing that we're going to know is whether you're pushed too hard because if you break the surface of the agar it's going to be very very obvious we want to make sure that none of the bacteria are going to survive so I go to pour some vidcon into my beaker and now any bacteria that were left on the spreader any bacteria that belong to the pipette in ten minutes those bacteria will be killed we know that the whole of the surface of the agar is covered in the culture of bacteria and those bacteria are going to start to grow and when they grow the colonies are going to merge together and we're going to have what is called a lawn of bacteria growing over the air gar play and that will make the surface of the agar plate cloudy just like the water with the culture in is very slightly cloudy you'll be able to see where the bacteria are growing so what we're going to do now is a bit of an experiment we're going to see can we stop those bacteria from growing and what we're going to use is we're going to use a disc that has been soaked and then dried but it actually has an antibiotic on it and that sort of antibiotic this one's actually streptomycin the sort of antibiotic that you would be given if you went to your doctor and your doctor gave you an antibiotic in order to kill bacteria we're also going to use one of my favorite substances because I like the smell of it is tea tree and we're also going to use a commercial antiseptic so this is the sort of thing that you see sold in shops for sterilizing surfaces and sterilizing hands and things and cuts so we're going to try to see what is best the antibiotic of the tea tree or the antiseptic so everything now we need to make sure all that we are still sterile and we also need to make sure that we know which disk is which so I'm going to call these 1 2 3 so on my plate pick it up without taking the lid off and going to write 1 2 3 so that I know where I'm going to put my little disks so ones going there too is going there 3 is going there 1 2 3 so we're going to have to open this again so we're going to turn this back on to blue flames so we create a lovely area of sterile there I'm going to start with the antibiotic disk and we're going to turn area number one towards the flame open pop it in on the dot and just push it down just a little bit so it stays there because you don't want it to fall off because I'll show you the problem you would have if you don't push it down in a minute now I'm going to take a disk or paper I'm going to soak it in tea tree oil that's tea tree rotate my plate so that position 2 is facing the flame open up just for the minimum amount of time put the disk going push it down so it stays and close the lid closing the lid as soon as possible as you do not want any contamination from around getting in now my third little one this is number three soak the disk in the commercial antiseptic rotate the agar plate open down press close stare up we need to incubate that and it's got to be incubated for long enough for the bacteria to grow but not so long that the whole thing is completely covered and just looks sort of generally unpleasant what we want to see is whether these discs will kill the bacteria and we'll know they'll kill the bacteria if we have a clear ring around the discs I wonder which one's going to be best one that is best is the one that's going to have the widest ring but is it going to be the commercial antibiotic for the tea tree or probably quite expensive antiseptic going to have to wait for a little bit to see we need to make sure that that lid doesn't come off just going to turn this Bunsen back to yellow and push it away but don't need the Bunsen burner on blue flame anymore because we no longer need to have sterile surroundings because now our bacteria are sealed in the agar plate we've got to make sure that the lid doesn't come off this is where the clear tape is going to come in I'm gonna see it seal the lid onto the petri dish with just two pieces of sellotape one either side now it might be tempting to think that what you need to do is to see it all the way runs the bacteria can't get out but if you seal it all the way around so the bacteria can't get out then oxygen can't get in and the coli that we put there won't grow but anything else that has contaminated this plate will grow and anything that's got in it from your hands from the desk from the air is likely to be an unpleasant bacteria and anaerobic conditions they will do really well in and the plate will start to get very smelly indeed so now we're going to store it and you're going to give this back to your teacher and your teacher is going to store this in an oven at 30 degrees centigrade until the bacteria started to grow when you'll be allowed to look at it again but we always store agar plates upside now this is a nervous moment because hopefully when I turn it upside down my disks don't fall off and hopefully when you turn it upside down your disks don't fall off there we are success so that now is upside down the reason we do that is any condensation will be on the lid not on the acre and it won't flow around and move all the bacteria away from the surface so that goes to your teacher and your teacher we'll put it in the oven and they'll know it's yours because you've got your name on it they'll know when it went in because you put the date on it don't know what's growing on it because you wrote in the name of the bacteria on it after that is gone your job is to disinfect your table so if you have accidentally spill Tony e-coli you're not going to spread them you coli around so the next person who comes in after you so a couple of days have passed and we need to return to our agar plate to see how things are developing what do you notice first of all if you have a look you can see that where the agar was completely clear it's now cloudy each part of that cloud is due to individual bacteria that you have spread evenly across the plate dividing by binary fission to reduce tiny little colonies which we are seeing now is cloudy area on the plate what you will see is that there are clear areas where the bacteria have not grown these are the clear areas where we put down our little disks this disk here is the antibiotic the commercial antibiotic and the other two with the cleaners that we chose this one is actually the tea tree you will see that there is actually a larger radius clear area around the tea tree the reason for these clear areas is that as the bacteria were growing on the rest of the plate they were not able to grow in the center around the disks because the antiseptic or the antibiotic was killing the bacteria now what can we do with this data to analyze this data what we could do is to measure the diameter of these clear areas that would give us a direct comparison of these different treatments in terms of how they are able to kill bacteria and we could do this for these plates and we could repeat it with another plate in order to repeated results or we could share results between the class there are a few things that we need to consider though was this actually a fair test the commercial antibiotic was dry the other two had been dipped in a liquid were those liquids of the same viscosity how is the antibiotic got through the agar so we need to consider that the only way in which the antibiotic could have got through the agar is through diffusion through the agar gel whereas the other two have they purely diffused out from the disks or could it have been the spreading of the wet substance over the surface of the disc so yes in this test there is a difference between them but does that test actually correctly reflect the ability of these substances to kill the bacteria one thing we need to consider when we do investigations like this is how can our results be applied to the wider world what circumstances would we do an investigation like this perhaps we would be interested to see which one of these would be better as a treatment to prevent the growth of bacteria that was causing an illness so let's think the commercial antibiotic is very effective it's the second best of the three tests that we've done this one the tea tree absolutely definitely the best but what we need to do is we need to ask ourselves if you've got a sore throat or a stomach bug that's been caused by this bacteria would you really want to be drinking tea tree so this practical which we've just demonstrated is quite a complex practical which is part of the new science GCSE if you want to have any extra training with any helps of the new science specification then Malmesbury school we're actually the home of the aden teaching school alliance and we run various courses which will support teachers and technicians with presenting practical science just like this if you want to know more about the work of the able teachers school alliance then follow the link in the description