Hi there, I'm Mrs. Kemp.

Welcome to today's lesson, all about the effect of antimicrobial substances on bacterial growth.

This part of the practical is the analysis and conclusions, and it fits into the medicines and new treatment for disease unit.

So let's get started then.

Our main outcome for today is, "I can compare the effectiveness of antimicrobial substances on bacterial growth on an agar plate by measuring the clear zones of inhibition." We will be using lots of new key terms today, and you can see some of those on the slide.

If you would like to pause and read those in more detail, please feel free, but rest assured that I will go over each one of them as we move through the slide deck.

So we've got two learning cycles for today: the data collection and analysis, and the importance in clinical settings.

Now, we really need our plates for this first part, the data collection and analysis, but don't worry if you don't have any from the practical.

Actually, there is some sample data that we can use on the worksheet.

So antimicrobials are actually substances that slow down or stop the growth of microorganisms often by killing them.

We can see here that we've got an agar plate that has a lawn of bacteria.

And in parts, that lawn of bacteria isn't there and that's where those microorganisms have been killed.

They are around those little paper discs because those paper discs we soaked in antimicrobial substances.

It enables us to be able to test and compare the effectiveness of antimicrobials.

So this is what, if you'd have carried out the practical, you will have set up something similar to this.

So how do we know which one is more effective than the other? Well, actually we can do that by that little zone around our paper disc known as the zone of inhibition because that is where the bacteria have been killed or prevented from growing.

And actually what will have happened is that that antimicrobial will have diffused, so moved out of the paper disc into that surrounding agar and that is then able to stop that bacterial growth.

The larger the area of the zone, the more effective the antimicrobial.

So just looking at those, you can see, well, which ones have and haven't got a zone of inhibition around them, and we can also see some of the ones that are larger.

Okay, true or false.

The discs were soaked in different types of bacteria.

True or false? Can you justify your answer? The discs were soaked in the same type of bacteria, or B, the discs were soaked in different antimicrobials.

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

Okay, that was, of course, false and that's because B, the discs were soaked in different types of antimicrobials.

Excellent.

Well done.

So we need to collect some data from our plates.

So we need to find out the area of those zones of inhibition because that will tell us the most effective antimicrobial.

Our paper disc is in the centre and you can see that zone of inhibition around it.

If we place a ruler against the zone of inhibition, then we can measure the diameter.

Sometimes, so as we can see in B and D there, actually the zone is not a perfect circle.

To overcome this, what we will do is measure the longest diameter, turn the ruler at 90 degrees and then measure the diameter again.

Add them up together and then divide by two and that will calculate a mean diameter and we would use that one for that particular zone of inhibition.

If like A, it's a perfect circle, then we would just measure the diameter once.

So to calculate the area of a zone of inhibition, we use this equation.

We use the equation for the area of a circle, which is pi times r squared.

R, remember is the radius.

The radius is half of the diameter.

So once we've measured the diameter, we need to divide that by two in order to work out the radius.

We can use the value of 3.

14 for pi if we do not have a scientific calculator with pi on.

Okay, let's have a go at it together then.

So Izzy measures the mean diameter of the zone of inhibition for an antimicrobial A to be 20 millimetres.

Can you use the equation pi r squared to calculate the area? Number one, we calculate r then and we need to square it where we multiply it by itself.

So r is equal to 20 divided by two, which gives us 10 millimetres.

We then have 10 times 10, or you can just use your square button on your calculator and that would give us 100 millimetres squared.

We can then multiply r squared by pi and we can use the number 3.

14 if we do not have pi on our calculator, and we get 314 millimetres squared, that is the area for that zone of inhibition.

Okay, can you have a go at this one yourself then? So Jacob measures the mean diameter of the zone of inhibition for antimicrobial B to be 18 millimetres.

Use the equation pi r squared to calculate the area.

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

So we calculate r and then square it.

So to calculate r, we do the diameter divided by two, which gives us nine millimetres.

We then times it by itself or we can just use the square button on our calculators to get 81.

We multiply that by pi, which is 3.

14, and that gives us 254.

34 millimetres squared for that zone of inhibition.

Now, because the first antimicrobial is 314, that is larger than 254.

34, that tells us that that antimicrobial is the most effective in this pairing.

Okay, you'll need to get your worksheets out for this next part.

It's our first task, Task A.

So if you have your plate from last lesson that has been taken out of the incubator, can you complete the table for your zones of inhibition? So we're first of all going to be working out that mean diameter by doing the two measurements, one for the longest, then turn it 90 degrees, and then measure it again.

We then add them together and divide by two.

You then need to work out the radius of that mean, so divide it by two, and then the area of that clear zone using pi r squared.

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

So hopefully you have now filled in that table with your own results.

However, the next part, we're going to use the results on our worksheets as sample data.

So if you didn't have any of your own results, then you can continue with this part anyway.

So use the sample data on the worksheet to calculate the radius of the clear zone of inhibition of microbial substance Y, so we can see it down there.

Calculate the area of the clear zone of inhibition for the antimicrobial Y.

And then tell me which of the four antimicrobials is the most effective and why.

You can use the sample data that is on there on that worksheet.

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

Okay, this is what your sample data will have looked like and you can find this on the worksheet.

So using that sample for antimicrobial Y, our mean diameter is 22 measured in millimetres.

The radius then is half of that, which is 11, and our area then when we work that out is 379.

9.

When we look at all four of those antimicrobials, the most effective is Y, and this is because it has the largest zone of inhibition around it, meaning it has killed the most bacteria.

I hope that you've got all of those calculations right, but please do go back over them if you were not quite there.

Okay, let's go on to our second learning cycle then, importance in clinical settings.

So some microorganisms have evolved resistance to antimicrobial substances, including antibiotics.

This is obviously quite worrying because we use these substances to make sure that pathogens are killed.

When this happens then, the antimicrobials are no longer effective at killing those resistant microorganisms or preventing their growth.

An example of a pathogen is gonorrhoea that is caused by a bacteria.

It's actually a sexually transmitted infection.

The bacteria that causes it will be passed during unprotected sex.

So when somebody has not used a condom, for example.

The bacteria has actually evolved resistance to multiple antibiotics that we had previously effectively used to kill it.

This includes penicillin.

Only a small number of antibiotics remain that are effective against this bacteria.

That causes a real problem then because it means that an easily treatable disease like gonorrhoea actually isn't quite as easy anymore and it could lead to major problems. The Oak pupils are discussing gonorrhoea.

Who is correct? Aisha suggests that gonorrhoea bacteria are now resistant to multiple antibiotics.

Lucas, "People should use protection during sex to prevent the spread of gonorrhoea." Sofia, "People shouldn't worry about gonorrhoea because it is easily treated with antibiotics." I'll give you a moment to think about it, but if you need more time, please pause the video.

Did you realise that both Aisha and Lucas are correct then? Gonorrhoea is a bacteria now resistant to multiple antibiotics and people should use protection during sex to prevent the spread of gonorrhoea.

Excellent, well done.

So there are some really important ways that we can reduce the spread of resistance to antibiotics in bacteria.

First of all, we need to avoid the overuse of antibiotics, especially when they might not be effective.

So if you go to the doctors and you're feeling unwell and they say, "Actually, you've got a viral infection," there's no way that that doctor would then provide you with antibiotics because actually the antibiotics can't kill viruses, and so therefore there isn't any point in using them.

Always use the most effective antibiotic to treat a patient who needs them, and that's why we would need to identify which bacteria it is in order to find out which is the most effective antibiotic.

To do this then, doctors do need to know how effective each antibiotic is at treating bacterial infections, and how they would do that then is a sample of bacteria would be sent from a patient into a lab in order to be tested.

They grow that bacteria on an agar plate and they would then use some different discs of the antibiotics on that plate to find out whether or not those different antibiotics are effective at killing that particular type of bacteria that has infected that person.

It's important that they use aseptic technique throughout the test to avoid contamination with other bacteria because the other bacteria may not be killed by the antibiotic, and therefore it would look like that particular antibiotic wasn't effective, or that bacteria might be killed by that antibiotic and so it looked like it was effective.

So it's really important that we make sure we're not contaminating our plate.

The growth of any other bacteria might obscure the clear zones then to affect the results.

Okay, onto another check.

Bacteria from a patient were grown on this agar plate.

Disc W was soaked only in water.

Disc A to H was soaked in different antibiotics.

Which two antibiotics would be the most effective at treating this patient? I will give you a moment to think about it, but if you need more time, please pause the video.

Okay, did you realise that it is E? Excellent.

That is our largest clear zone, and G is our second largest, and therefore would also be effective at killing that bacteria.

Well done.

Which two antibiotics then are the bacteria resistant to? 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 A and also C? Excellent.

Well done.

Okay, onto our next task then, this one is Task B.

A patient is infected with a type of bacteria called Staphylococcus aureus.

Now, some strains of this bacteria are known as MRSA, that stands for methicillin, which is a type of antibiotic, resistant Staphylococcus aureus, that particular type of bacteria, and that is because they're resistant to various types of antibiotic, including methicillin.

Methicillin is a very, very strong type of antibiotic, which usually kills everything, and it's usually only prescribed in hospitals.

If that one doesn't work, then it's a really tricky disease to get rid of.

We can see that on there that there is an image of MRSA observed using a microscope.

So can you describe how an agar plate could be used to find out which antibiotics should and should not be used to treat this patient's staphylococcus Aureus infection? Also, can you explain why it is important to use aseptic technique throughout the tests? I'll give you a moment to think about it, but if you need more time, please pause the video.

Okay, let's go to number one first then, describing how an agar plate can be used to find out which antibiotics should or should not be used to treat the patient's Staphylococcus aureus infection.

So first of all, take a sample of the Staphylococcus aureus bacteria from the patient.

Grow that sample as a lawn on an agar plate in culture.

Add antibiotic discs to the bacteria and culture the plate again.

Compare the sizes of any clear zones of inhibition around the discs, so that's when we would use our pi r squared in order to calculate the zone of inhibition.

The larger the area of the zone, the more effective the antibiotic is at killing the bacteria and stopping their growth.

The most effective antibiotic should be used to treat the patient.

They might actually need a combination of different antibiotics in order to make sure that they actually kill that infection.

If there is not a clear zone around a disc, the bacteria are resistant to the antibiotic and it should not be used to treat the patient.

We would not use that particular one in order to treat them, but we might use one or more than one of the others.

So explaining why it is important to use aseptic technique throughout the tests.

It's important to use aseptic technique throughout the test to avoid contamination with other bacteria.

The growth of any other bacteria might obscure the clear zones and affect the results.

This could lead to the wrong choice of antibiotic being used to treat the patient.

This would obviously have been a major issue then because actually if you have gone and prescribed a different drug for a particular patient and then it doesn't work, that patient could get more sick than they would've done if you just managed to treat them straight away.

Okay, we're very close to finishing.

We're just going to go through the key learning points for today.

So not all antimicrobials are equally effective at killing bacteria.

The effect of antimicrobials on bacterial growth can be tested and compared using paper discs soaked in different antimicrobials added to bacteria on an agar plate.

The areas of clear zones of inhibition can be calculated using pi r squared and compared to investigate antimicrobial effectiveness.

The larger the clear zone, the more effective the antimicrobial has been in killing the bacteria and stopping their growth.

It is important to test antimicrobials, including antibiotics in clinical settings to help reduce the spread of resistance.

I hope you've enjoyed today's lesson, I certainly have, and I hope to see you again soon.

Bye now.