Download Growing up Bacteria lesson plan

Growing up Bacteria lesson plan
Summary
Students use agar plates and a home-made incubator to grow bacteria from the school
environment.
Learning outcomes
Students learn about what bacteria are, what they need to live as living organisms, where they
live in the school, and how they can affect health.
Components
1.
2.
3.
4.
5.
6.
Introduction – what is a germ? What are bacteria?
Explanation of activity: what is agar? How do we grow up bacteria?
Creating the incubator
Sampling surfaces for bacteria
Growing up the bacteria
Discussion
Before you start: Talk to your local health workers and environmental health workers
about working together on this lesson. Ask if you can dispose of the
agar plates with the clinic’s infectious waste. This lesson ties in nicely
with the Mr Germ Program, run by Environmental Health Units.
Materials needed:
Agar plates
Cotton buds
A permanent marker
Sticky tape
Styrofoam or plastic box
A small lamp
A plastic sheet or a couple of A4 plastic
sleeves
1. Introduction – what is a germ? What are bacteria?
Health workers talk about germs a lot, but what are germs? What are the different kinds of
germs?



Bacteria (e.g. Salmonella)
Protozoa (e.g. Giardia)
Fungus (e.g. Ringworm)
www.amrric.org
Bacteria are a family of tiny living things, too small to see with our eyes alone. They are
smaller than a grain of sand. You can only see them with a microscope.
But, just like when you have lots and lots of grains of sand all together, you can easily
see the beach: when there are lots and lots of bacteria together, we can see their group
or ‘colony’.
Bacteria live in lots of places: in soil, on skin and in the gut. There are a lot of types of
bacteria that live around us: Staphs, Streps, E. coli, Salmonella. Some are good and
helpful, and others can make us sick, like with diarrhoea, skin sores, kidney infections
and blood diseases.
Today we are going to take some of the bacteria that live around us and grow them on
special plates called ‘agar plates’. The bacteria will grow and multiply, and if we look
after them right, we will be able to see the colonies after a few days.
Extension exercise: Zoonoses lesson plan and activity sheet
Extension activity: ask one of your health workers to give a talk about a bacterial
disease that is important in your community
2. Explanation of activity: what is agar? What is an incubator?
Because bacteria are tiny living things, they need the same sorts of things that we do to stay
alive and healthy and grow:
-
Food
Water
Warmth
Shelter
Company
If we give them all these things they will grow and multiply.
The agar plates will help us give them food, water and shelter. Agar is a kind of jelly made
specially for bacteria. It gives them all the food they need to grow really well, and stops them
from dying of thirst too. The plate gives them shelter, stopping them getting squashed or
scraped by something on top, and helping to keep the water in.
An incubator is a special box to keep them warm. Bacteria grow and multiply best when they
are warm and moist.
Bacteria like company to feel good and multiply. When we collect bacteria from the things
around us, we try and get a good sample, not just one or two, so they’ll make a big family.
www.amrric.org
How to put the bacteria onto the agar
Getting bacteria and putting them on the agar is called ‘sampling’. We need to make sure we get
only the bacteria from the place we are interested in. We don’t want to get the bacteria from
our hands on every agar plate: we want to grow up different kinds of bacteria from different
places. So we use cotton buds to take the bacteria from a surface, and then wipe them onto the
agar. Then we put the lid back on the agar plate and sticky tape it shut, to keep the moisture in
and to stop the plate opening by accident. Then we need to write on the bottom of the plate
what surface we sampled, so we can remember where the bacteria came from.
3. Creating the incubator:
Materials:
Styrofoam (or other flame retardant material) box
Sheet of plastic, such as an A4 plastic sleeve
Small lamp
Put the box on its side so you can see inside. Put the lamp inside the box and turn it on. Sticky
tape the plastic sheet to the top of the box so it covers the side opening.
If you have a thermometer, put it inside the incubator too. Bacteria like it around 30-35 degrees
Celsius. If it’s cooler, they will grow more slowly (that’s why we keep food in the fridge: to stop
bacteria growing on it). If it’s too warm, they might dry out and die.
4. Sampling surfaces for bacteria
Have a think about where bacteria might live: In rain puddles? In the toilet? On skin? In snot? On
dog’s coats? In dog’s poo? On the computer keyboard? If you like, think of two surfaces to
compare: for example, dog coats and human hands, dog’s tongues and human spit, dog poo and
the toilet. That way you can see which one has more germs. When you know which surfaces
you want to sample:
1.
2.
3.
4.
5.
Wipe the cotton bud a few times on the surface you want to
investigate. Remember not to touch the tip of the cotton bud with
anything else.
Lift up the lid of the agar plate a little and wipe the cotton bud on
the surface of the agar. Don’t wipe too hard or the agar will
break!
Close the lid, and sticky tape it shut.
Write on the bottom of the plate what surface you sampled.
Wash your hands!
Then put all the agar plates in the incubator.
Try and keep one agar plate to use as a ‘control’. This is one that you don’t wipe any bacteria
onto. Sticky tape it shut and put it in the incubator. This one shouldn’t grow any bacteria: you
can compare it to the others later.
www.amrric.org
5. Growing up the bacteria
Keep the light in the incubator on all the time: it is keeping the bacteria warm. Keep the cover
closed most of the time, to keep the moisture in. Check the bacteria once or twice a day to see if
they are growing.
You will know if the bacteria are growing because it will start to smell bad! Bacteria make gas
as they grow: that’s why old sweaty socks smell, and rubbish smells bad too.
After about three days you should be able to see little dots on the agar: these are the bacteria
colonies!
6. Discussion
Look at all the plates and compare which ones grew lots of bacteria and which ones didn’t.
Sometimes bacteria won’t grow if it’s too dry, e.g. if the agar dried out and cracked. Bacteria
also don’t like soap, so washed hands and cleaned toilets are usually pretty clean! Floors and
puddles are usually good sources of bacteria, as are dogs’ coats because they lie on the floor.
Poo is a great source of bacteria because lots of bacteria live in the gut to help us digest our food.
-
Make a list of places where there were lots of bacteria
-
Make a list of places where there weren’t very many
What can we do to make sure we don’t get sick from bacteria?
Extension option: write up the activity as a science experiment under the headings: Research
Question, Methods, Results, Conclusion
www.amrric.org