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Bacteria: live specimens

Understanding bacteria with agar plates
Useful information
Kit List: 

*NB: None of this stuff currently exists
- Agar plates with 4 different types of bacteria (lab attenuated, of course!)
- Pictures and posters on walls.
- Easy-to-use slide viewers with pictures of bacteria in them (v suited to small kids)
- Microscope and gram-stained bacteria and yeast slides (v suited to older kids).
- Goodies for kids!


Bacteria can be very exciting and this experiment should help kids to understand a bit more about what we mean by "germs".

*** OVERVIEW ****

A display of different bacteria and how they interact with us!

Possible activities:
1. Verbal explanation - what are germs?
1. Looking at colonies on the Petri dishes. Agar, differences between colonies.
2. Looking at the slides. Bacteria are small.
3. Verbal explanation of the displays. Diseases and harmless/useful bacteria.

Other things to talk about:
- General discussion on bacteria/germs/viruses/microbiology.

Tips for demonstrating:
1. Follow the risk assessment to keep control of the bacteria and slides.
2. Find out what each display is showing. Visitors expect YOU to know everything on the board/slide/Petri dishes.
3. Be prepare to challenge misconceptions: e.g. All bacteria are bad for you; myths about GM organisms, etc.


One way to go about teaching this might be to start with asking kids what we mean by germs - I imagine the word "bacteria" will come out eventually. Where are bacteria? All over the place, especially on our food, in our tummies, on the floor when it's not been cleaned with bleach etc.

Then look at the colonies - ask what the kids think they are. Do they see colonies in their house? Probably not like these. Agar is great food, so that's why we see so many bacteria. We use agar to see the colony size and shape, which tells us lots of info about what sort of bacteria we are looking at. Can they describe colonies? (colour, size, shinyness, shape)

Now, we can also look at individual bacteria, which are really small. Most are minute, usually only 0.5-5.0 μm in their longest dimension, although giant bacteria like Thiomargarita namibiensis and Epulopiscium fishelsoni may grow past 0.5 mm in size. 5 micrometres means that 200 of them could fit into 1 mm. That's why we can't see them. So we can use microscopes to look at them.

Pictures of many different species of bacteria are on display. Many are disease causing and you can talk about the diseases they cause. Don't forget to mention that most bacteria are harmless to human (even though there are hundreds of pathogenic species of bacteria, but compare that to the total number of species of bacteria - many thousand million species as estimate.). Some bacteria are good for you: Lactobacillus in probiotics, for example. Your normal flora have can prevent pathogens from colonising, produce vitamin K, help digestion.


General microbiology.

Gram staining and ways to distinguish between different bacterial species.

Bacteria that live in extreme environments.


Risk Assessment
Date risk assesment last checked: 
Wed, 25/12/2013
Risk assesment checked by: 
Date risk assesment double checked: 
Wed, 01/01/2014
Risk assesment double-checked by: 
Risk Assessment: 

Note: Requires serious consideration of microbiological handling facilities, needs PhD student in appropriate department and consideration of transport.

DESCRIPTION Colonies of micro-organisms in petri dishes (these will be some/all of the following):

1. Micrococcus luteus (On Nutrient agar)

2. E. coli K12 (On Nutrient agar)

3. Janthino lividum (On nutrient agar)

4. Neurospora crass (fungus, one nutrient agar

5.. 'Good bacteria' from brand A bioyoghurt drink (On chocolate agar)

6. 'Good bacteria' from brand B bioyoghurt drink (On chocolate agar).

8. Staphylococcus aureus (On Blood agar)

Slides of many micro-organism, Gram stained, mounted onto slides (these will be some/all of the following):

1. Staphylococcus aureus
2. Streptococcus pyogenes
3. Clostridium tetani
4. E. coli
5. Salmonella
6. Corynebacterium
7. Bacillus
8. Candida albicans

Also, "biovewers" - simple to use "microscopes" with the experiment for looking at bacterial slides. Wall-mounted poster display.

  • 1. Sharp edges of slides may present cutting risk. Slide may be dropped and the broken glass may also present cutting risk. No risk from organisms fixed on the slides as the staining process would have killed the cells.
  • 2. Electrical equipment - hot and risk of electrocution if faulty.
  • 3. Accidental exposure of micro-organisms/blood agar if Petri dishes are broken/stolen/lid removed.
  • 4. Risks of infection during sample preparation (pre-event).
  • 5. Risks of infection after event due to incorrect disposal.
  • 1. Ensure that the demonstrators are well briefed about the potential risks and keep a close eye on Petri dishes. Children are not allowed to handle the Petri-dish or slides. Sign should be on display saying "Don't touch! Live bacteria." Demonstrator to ensure that a sharps bin is located nearby to dispose of slides should they break.
  • 2. Switch off microscope between uses if it starts to become hot. Ensure experiment is not near a watery experiment.
  • 3. Secure the pathogenic (Staphylococcus aureus, and both yogurt cultures) Petri dishes (which are sealed with parafilm) onto a display board with clear plastic laminate that goes over the plates, and makes them very hard to run away with. Venue safety officer to ensure "safe" micro-organsisms are used - will help. Non-pathogenic (#1-4) organisms must still be sealed in parafilm, and secured with string to the table; however, these do not need to be covered in plastic laminate.
  • 4. Standard lab procedures to be obeyed. The person preparing the agar plates must have had experience in working with bacterial plates.
  • 5. Demonstrator must not throw old petri dishes into the bin. Petri dishes must be autoclaved after use (the dishes can be left in a tied up petri dish/biohazard bag for 2 days max until they can be brought to an autoclave). Venue safety officer to ensure these provisions are in place.
  • 1. Wash any small cuts with soapy running water. Compress and elevate large cuts. Call a first aider. If an agar plate was broken, cordon off area, remove glass/plastic, clean area thoroughly with disinfectant and alcohol. Warn parents to watch the cut and to attend GP or A+E if there is a change in appearance to the wound which they think is odd, eg. pus or lots of redness.
  • 2. Switch off electric equipment in event of an electric accident, call a first aider, give the casualty space. In the event of a burn, hold area under cold water for at least ten minutes. Call a first aider.
  • 3. See 1.
  • 4. See a GP if symptoms develop which the person thinks may be related to preparing the plates.
  • 5. Inform department if plates have been erroneously disposed of, try to relocate plates in order to autoclave them.
  • This experiment contains mains electrical parts, see separate risk assessment.