Hi there, I'm Mrs. Kemp and welcome to today's lesson all about the effect of antimicrobial substances on bacterial growth.

This one is a practical lesson and it fits into the unit of medicines and new treatments for disease.

So let's get started then.

Our main outcome for today is I can use aseptic techniques to investigate the effect of antimicrobial substances on bacterial growth.

We will be using lots of key terms and you can see some on the board for you here.

And if you'd like to pause and read those in more detail, please do that now.

But do rest assured that I will go over these as we move through the slide deck.

We've got two learning cycles, which are aseptic technique and the effect of antimicrobials on bacterial growth.

Of course, we will start with aseptic technique.

So actually all around us all the time, there are actually millions of microorganisms, including things like bacteria, viruses and fungi.

They're in the air, they're on all the surfaces, and most of the time they have no effect on us and we don't worry about them at all.

However, if you are a microbiologist or a scientist that is working with microorganisms, actually you want to make sure that you work in an environment without these bacteria and viruses and fungi.

And in order to do this, we use a practical method known as aseptic technique.

The technique will reduce the risk.

So whether or not something is likely to happen of contaminating yourself, so the person that's actually doing the practical, your work environment around you.

So that would mean that when other people come into that area, they might get contaminated.

And also we don't actually want our samples, so the microorganisms that we're working with, to be contaminated with anything that is in the environment.

Okay, onto our first check.

Which practical method reduces the risk of contamination with microorganisms? Is it A, antigen technique, B antibiotic technique, or C aseptic technique? I'll give you a moment to think about it, but if you need more time, please pause the video.

Okay, did you realise that it's C, aseptic technique? Excellent, well done.

So we're going to have a go at using aseptic technique in order to grow some bacteria on an agar plate.

An agar plate is just a Petri dish, so it could be plastic or glass.

And inside it there is a growth medium, which is a solidified agar jelly.

It does feel very, very similar to the jelly that you eat, but we don't eat this type of agar.

It can be used to grow a culture then, a culture of microorganisms in a warm incubator.

The incubator is a little bit like a sort of oven if you like, that just warms it to a nice temperature.

All equipment needs to be sterilised first.

So without microorganisms, and the way that we do that often is it needs to be heated to quite high temperatures and you can use something called an autoclave, which will steam and heat that equipment to really high temperatures so we can make sure that we've got rid of any of those microorganisms that are in the environment.

We also want to make sure that we work really closely next to a Bunsen burner.

Now the Bunsen burner heats up the air around it, which means that you get an upward flow of air all the time.

This prevents microorganisms from being able to get into your working area and settle and essentially prevents it then from having any microorganisms in that area.

Okay, true or false? And autoclave is used to grow the bacteria in culture.

Is that true or is that false? Of course that one is false.

Could you justify your answer then? A, an autoclave heats the bacteria to a temperature suitable for growth.

B, an incubator is used to keep the bacteria warm and provide the correct conditions for growth.

I'll give you a moment to think about it, but if you need more time, please pause the video.

Okay, did you realise that it was B, an incubator is used to keep the bacteria warm and provide the correct conditions for growth.

Well done, okay.

Let's have a look at a method then for preparing that agar plate.

So that Petri dish that's got the agar jelly in it, to grow bacteria using our aseptic techniques.

So making sure that the environment is completely sterile.

Some safety advice here then, we will be using a Bunsen burner.

So please can you make sure that you tie any long hair back? We tuck in any loose clothing and we make sure that we wear safety goggles to prevent any contamination into our eyes.

So first of all, make sure that you have washed your hands at the start.

This will make sure that if you've got any microorganisms on your hands, they're as clean as they can be.

We might not get rid of every single one, but we'll get rid of the majority.

Second thing then, we spray and wipe all the surfaces with disinfectant to kill any microorganisms that are there.

But if safety advice for this then, do not spray disinfectant near the lit Bunsen and burner as actually, it could be flammable.

Safely like your Bunsen burner.

So you're making sure that the hole is closed and you keeping it at arm's length so that it's lighting it on that safety flame, on that yellow flame.

Number four, label the underside of the agar plate with your initials and the date and the name of your bacteria.

Okay, so then when they go into the incubator later, we can identify actually what's on that plate and who it belongs to and when we put it in.

Okay, we are now going to watch a little video to show you how to do this.

Okay, method for then adding the bacteria to the agar plate.

So we've already labelled our plate and it's ready to go.

We've got to use aseptic technique now in order to make sure that we grow what we want.

So first of all, working closely near that lit Bunsen burner, we put a wire inoculating loop.

We can see one in that image there, and we put that into the flame just until it glows red.

We then need to wait just a moment for that loop to cool, okay? Because if we use it when it's boiling hot, it's likely to kill the bacteria that are in our sample.

So we need it to cool down first.

We then open the bottle of bacteria and we pass the neck of the bottle through the flame.

Okay, so you just pass it through once or twice.

Safety advice then, flaming the top of the bottle will stop bacteria from escaping and contaminating the environment.

So we don't want an aerosol of that bacteria to go out into the atmosphere and environment.

That's why we pass it through the flames.

So it would kill any that that was happening to.

We then dip the inoculating loop into the bacteria and remove it and you'll get like a little film of bacteria and solution and the media that it's in essentially, in that little loop part.

You then flame the bottle again and replace the lid.

You do have to be careful there because it can get quite hot the more times that you pass it through the flame.

So do be careful.

Lift the lid of the agar plate to a 45 degree angle.

You can see the image there of that lid being lifted so it's not being lifted fully open.

It's only being lifted part open, okay? And that's to help to prevent any contamination inside your plate.

You then use your loop to gently streak across the bacteria.

Remember that agar is very much like jelly, okay? If you push too hard, it will pierce the surface.

We just gently want to almost tickle it across that agar jelly just to make sure that we are not damaging the surface of the agar.

We then replace the lid really quickly.

We then put the inoculating loop back through the flame again, till it grows red, and that will sterilise it.

So any bacteria that you had on it whilst you were doing the street plate actually now will be killed.

We use two pieces of sticky tape to attach the lid to the plate and incubate at 25 degrees Celsius for 24 hours.

It's important in schools that we don't incubate our bacteria to any higher than 25 degrees because we don't want to grow any pathogenic microorganisms. We only seal the lid just on the two sides of the tape.

And the reason why we do that is so that actually oxygen can still get in for those microorganisms. Okay, we're going to watch a little demonstration of this now on the video.

So the two pieces of sticky tape that hold the agar plate then, this prevents the lid falling off.

Okay? So it reduces the risk of any contamination to the environment, but we don't seal all the way around.

That would mean that we would prevent oxygen entering the plate.

Bacteria, just like other organisms, they need oxygen to grow and they need it for respiration, and that's aerobic respiration.

If there's no oxygen in there, we've got much higher chance of growing an aerobic bacteria, which actually are usually more dangerous.

We incubate a maximum of 25 degrees Celsius in schools, and that's to prevent the growth of pathogens.

Remember that pathogens are microorganisms that cause disease.

Okay, so why does working next to a lit Bunsen burner help to reduce contamination? A, it creates an upwards flow of air, B, it sterilises the work surface.

C, it prevents bacteria from escaping their container.

I'll give you a moment to think about it, but if you need more time, please pause the video.

Okay, did you realise that it's A, it creates an upward flow of air.

Excellent, well done.

Okay, onto our first task of the day then, task A.

You can get your worksheets out to record your answers.

Can you join each example of aseptic technique to its purpose? Washing hands, spraying disinfectant, flaming the inoculating loop, flaming the neck of the bottle.

Lift the plate lid to a 45 degree angle, kills microorganisms on the work surfaces, sterilises the wire to avoid contaminating the bacteria bottle, removes microorganisms from the skin, prevents and wanted microorganisms from settling on the agar and prevents bacteria contaminating the air.

I'll give you a moment to think about it, but if you need more time, please pause the video.

Okay, washing hands removes microorganisms from the skin.

Spraying disinfectant kills microorganisms on work surfaces.

Flaming the inoculating loop sterilises the wire to avoid contaminating the bacteria bottle.

Flaming the neck of the bottle prevents bacteria, contaminating the air and lifting the platelet to a 45 degree angle prevents unwanted microorganisms from settling on the agar.

Onto our second part of the task.

Can you write a risk assessment for adding bacteria to an agar plate to grow in culture? I've already put an example on there for you.

So there's a hazard, a risk and a precaution.

One hazard was the Bunsen burner.

The risk is burning yourself or other things.

Precautions, tie long hair back, tuck loose clothing in, place the Bunsen on a heat proof mat, return to a safety flame when not in use.

I'll give you a moment to think about it, but if you need more time, please pause the video.

Okay, did you get using flammable disinfectant, the risk, catching fire, precaution do not spray near a lit Bunsen burner.

Hazard, using live bacteria, contaminating ourselves, our workspace or the sample of bacteria with unwanted microorganisms, aseptic techniques, wash hands and disinfect work benches.

Flame the inoculating loop and the mouth of the bottle.

Open the agar plate to a 45 degree angle and tape the lid onto the plate.

You may have thought of some others and you can discuss these if you wish.

Okay, onto our next learning cycle, the effect of antimicrobials on bacterial growth.

So we can investigate the effect of antimicrobial substances.

So substances that will kill microbes such as antibiotics and antiseptics on bacterial growth using that agar plate with an evenly spread lawn of bacteria.

So instead of having streaks on the plate, it's actually just a full lawn of bacteria across the whole thing.

In order to do that, then we're going to need our Bunsen burner, an agar plate with the bacteria lawn already on it, a ruler, a permanent marker, some disinfectant in a beaker, forceps, paper discs and tape.

So make sure that you have collected all of your equipment ready.

Which pieces of equipment do we need to investigate the effect of antimicrobials on bacterial growth? A paper discs, B, a crucible or C, agar plate.

I'll give you a moment to think about it, but if you need more time, please pause the video.

Did you realise that it's both paper discs and agar plate? Excellent, well done.

Okay, so we're going to use an agar plate then that has a total bacterial lawn all across it like we can see in the picture, and we're going to investigate the effect of some different antiseptic solutions on that growth.

Okay, and we will use some little paper discs.

You can see them on the agar plate there, that have been soaked in an antiseptic.

Around each one of those paper discs then, what we will get is a clear zone and that clear zone shows where the bacteria have been killed.

Obviously the larger that clear zone then, the more bacteria has been killed.

We've got an independent variable and that is the type of antiseptic.

So we are going to change that particular variable and we will have different examples and you may have totally different examples to other people.

Our dependent variable then is the size of that clear zone.

'Cause that's going to tell us how many of the bacteria that antiseptic is actually able to kill.

We will need to control some things, the incubation temperature.

So we're going to be using 25 degrees, the time and how long it's being incubated for, usually 24 hours.

Can you think of any others? Things like the size of the paper disc, how long we soak the paper disc for, things like that will also have an effect.

Okay, what is the dependent variable in this investigation? A incubation time, B type of antiseptic or C size of clear zone.

I'll give you a moment to think about it, but if you need more time, please pause the video.

Okay, size of the clear zone.

Excellent, well done.

So method for testing the effect of an antiseptic solution on the growth of that bacteria then.

First of all, because we're using bacteria, we need to make sure that we've washed our hands to make sure that they are as clean as possible.

We will mark the underside of the agar plate with our name.

So just your initials are fine.

The date and the type of bacteria that has been streaked on the plate.

You can see around that labelled agar plate, it's written at the very, very edge of that plate, and that means that you can still see what's on the plate itself.

We need to divide the underside of that plate into however many sections you wish.

This one's being marked into quarters because we're using four different types of antiseptic.

Make sure you have the same number of sections as your antiseptics that you are testing.

So if you are using more or less than four, you will need more or less sections.

Label each section that you can clearly identify which antiseptic is in which bit.

I've put one, two, three, four, and then they would correspond to the type of antiseptic.

Draw a dot in the middle of each section so you know where your paper disc is going to be placed.

Okay, we need to sterilise our forceps first of all.

So we will pass those through the Bunsen burner flame and then allow them to cool.

Using our forceps then, we pick up a paper disc and we dip it into the antiseptic solution.

We carefully shake off any excess solution and then we place it on the agar plate.

Remember that jelly is like a jelly, and therefore if we push too hard, we'll break the surface.

So we just want to lightly push them on.

Carefully lift the lid of the agar plate only to that 45 degree angle.

This will prevent contamination from the air onto the plate.

Do not take the lid off fully.

Place the paper disc on that dot then very gently and carefully, and then you are ready to go for your next one.

So we repeat steps six to nine with each of the antiseptic solutions, making sure to sterilise your forceps in between.

So once we've done all four, we then use two pieces of sticky tape to attach to the lid.

Okay, and remember, we are just sealing it at the sides, not all the way around, so that we're creating every bit conditions for our bacteria to grow in.

We then incubate the agar plate upside down, okay? The reason why we put it upside down is that actually it prevents any contamination from settling on the actual agar plate itself.

It then collects on the lid and it reduces the risk of any contamination.

We are going to be storing them at 25 degrees for 24 hours.

We can watch a video clip to understand how to carry this process out.

Okay, two students talk about how to incubate their bacterial plates in school.

Is Sam correct? Laura says, at what temperature should we incubate our plates? Sam says, 40 degrees as it's closest to body temperature.

What do you think about that? I'll give you a moment to think about it, but if you need more time, please pause the video.

Did you think that this is incorrect then? Remember that we want to really incubate them at 25 degrees.

Okay, can you identify two variables that need to be controlled during the investigation? Can you follow the method on the worksheet to set up your agar plate with bacteria and antimicrobial disc to be cultured, ready for next lesson.

Make sure you use aseptic technique as we have discussed.

I'll give you a moment to think about it, but if you're going to be doing the practical, you will need to pause the video.

Okay, some variables that could have been identified then, you may have picked two of the following variables that need to be kept the same for each antiseptic.

Incubation temperature, incubation time, type of agar growth medium, concentration of antiseptic, size of paper disc, type of bacteria.

Excellent, well done.

Okay, we're very close to finishing then, hopefully you've got your plates ready for next lesson.

And what we are going to do is we're just going to go through some of those key learning points from today.

When using samples of microorganisms, scientists must take care not to contaminate themselves, their work area or their samples, to prevent contamination they use aseptic technique, using aseptic technique, scientists can grow bacteria on agar plate.

Scientists can place discs soaked in antimicrobials on an agar plate with bacteria to investigate their effects of bacterial growth.

I've really enjoyed today's lesson.

I hope you've learnt a lot, I'll see you again soon, bye.