1. Unit 1 – Living Cells Topic 2 – Microbes! Types of Microbes
Controlling the growth of microbes
Microbes in industry

2. Controlling the growth of microbes LEARNING OUTCOMES
Name 2 characteristics about how microbes grow and reproduce
State what antibiotics do
State what antifungals do
State what antivirals do

3. Think / Pair / Share You have seen microbes grow on agar dishes
These dishes have now been destroyed
What would happen to the microbes if we left them in the incubator?
Why do you think we should control how microbes grow?
How do you think we can do control the growth of microbes?

4. Microbial Growth
Microbes, such as bacteria and yeast, have many characteristics that help them to reproduce, such as being able to reproduce asexually and grow rapidly.

5. Controlling the growth of Microbes 1
Microbes need a suitable temperature to reproduce.
Placing microbes in cold temperatures (fridge) slow down the growth of microbes.
Placing microbes in very hot temperatures (oven) can destroy microbes.

6. Controlling the growth of Microbes 2
Special chemicals can be used to PREVENT the microbes from growing any further.
These chemicals can be found in:
cleaning products such as bleach or disinfectant or
in medicinal products like:
AntiBiotics are used to treat Bacterial infections (bacteria)
AntiVirals are used to treat Viral infections (viruses)
AntiFungals are used to treat Fungal infections (fungi)

7. Alexander Fleming (1881 –1955)
The Discovery of Penicillin and Antibiotics VIDEO (2.20 mins)

8. Alexander Fleming (1881 –1955) we now call them antibiotics.
Alexander Fleming accidentally discovered penicillin (an antibiotic)
He was throwing out old mouldy bacterial cultures when he noticed that they had clear areas around the mould
He concluded that the mould was secreting a chemical that was killing the bacteria
He isolated the chemical
The mould was called Penicillium so he called the substance penicillin
Fleming’s discovery led to the discovery of many similar substances
we now call them antibiotics.

9. Antibiotic Disk
Bacteria can be grown all over nutrient agar in a petri dish
Then an antibiotic can be added. Antibiotics stop bacteria from growing.
Antibiotic
NO bacteria growing
Bacteria growing

10. Clear zone (NO bacteria growing)
Diameter of clear zone

11. Antibiotic Multi-disks
We can use SEVERAL antibiotics to see which one is more effective at stopping the growth of bacteria.

12. Antibiotic Multi-disks
Aim: To investigate… Measurements to be made:
Which antibiotic is more effective at stopping the growth of bacteria
The diameter of the clear zone,
in cm,
using a ruler

13. Antibiotic Multi-disks
Results: Conclusion:
(answer your aim and link in your results)

14. Antibiotic Multi-disks
Results: Conclusion:
Antibiotic
Diameter of CLEAR ZONE (cm) P S TE C E G
Antibiotic ____ was the most effective at stopping the growth of the bacteria because it had the ______ clear zone.

15. Controlling the growth of microbes LEARNING OUTCOMES
Name 2 characteristics about how microbes grow and reproduce
State what antibiotics do
State what antifungals do
State what antivirals do

17. Controlling the growth of microbes LEARNING OUTCOMES
Explain what is meant by ‘resistant’ bacteria
Explain what is meant by ‘sensitive’ bacteria

18. Resistant Vs Sensitive bacteria
Region of bacterial growth
(Bacteria is resistant here)
Not all antibiotics are as effective as each other.
What is the best antibiotic?
What are the worst antibiotics?
‘best’ and ‘worst’ are not scientific terms.
Instead we can use ‘resistant’ and ‘sensitive’
Region of no bacterial growth
(Bacteria is sensitive here)

19. Resistant Vs Sensitive bacteria
If bacteria is prevented from growing it is said to be sensitive to the antibiotic
And if the bacteria is not affected it is said to resistant to the antibiotic.
From the antibiotic multi disk diagram,
the bacteria is resistant to antibiotics _______
And the bacteria is sensitive to antibiotics _______
P and E
G, S, C and TE

20. Antibiotics / destroyed / resistant / over-use
Resistant Bacteria
Resistant bacteria are not killed by antibiotics.
This is because the bacteria are too ‘strong’ to be destroyed.
More and more bacteria are becoming resistant to antibiotics.
The main reason is because we over-use them!
Antibiotics / destroyed / resistant / over-use

21. Controlling the growth of microbes LEARNING OUTCOMES
Explain what is meant by ‘resistant’ bacteria
Explain what is meant by ‘sensitive’ bacteria