Where can we find bacteria?

Where can we find bacteria?
How can you find bacteria?
• You can’t see it, so how do you find it?
• Under the right conditions, bacteria grows very fast,
• Some bacteria populations can double every 10
• Bacteria grow in colonies – a colony is a visible mass of
bacterial growth on solid medium that developed from
1 or a few cells
• A colony can contain millions of cells
• We can find bacteria by growing it in the right
conditions until it is visible to the human eye
Growing/culturing bacteria
• Conditions – temperature, light
• Agar – source of nutrients for growth
– From Malay word “agar-agar” meaning jelly
– Gelatinous substance made from seaweed
– Ingredient used in Japanese desserts
Lab Today
• We’ll look for bacteria and fungus around the
classroom and school
• Make a hypothesis about where you will find
the most bacteria
• Describe your methods
How to Sample Bacteria
2 Samples
3 Samples
4 Samples
• Get a Petri dish
• With a marker, divide it into 2, 3, or 4 equal parts
How to Sample Bacteria
• Write on the
bottom side (side
with the agar)
• Write small and around the edge so you can
see the bacteria growing later
• Decide where you will sample and label your
Petri dish accordingly
How to Sample Bacteria
• Get a sterile swab – don’t touch the cotton end
• Swab the area to be tested
• Open your Petri dish carefully and swab the
cotton in the specified area on the agar
• Close the Petri dish quickly
• Get a new swab for each sample
• When done, close the Petri dish and use Parafilm
to seal the sides
• Put the Petri dish upside down in a dark, warm
Photo Credits
• Slide 1 (Title): http://www.norcalblogs.com/ and
• Slide 3:
and masak-masak.blogspot.com/ 2007_09_01_archive.html
• Slide 5:
• Slide 6:

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