2-3 Making a medium - You try it

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Making medium is as simple as cooking and a crude medium can be made in almost any kitchen with a few utensils and a source of heat. Below is described the production of a chicken broth medium that will grow many common microorganisms. The medium will be sterilized by tyndalization. Simply boiling a medium once, while it will kill most vegetative cells, does not kill endospores. However, heating encourages the endospores to germinate, and a second boiling kills these microbes. The boiling process is repeated a third time to ensure that all spores have germinated and been killed.

  1. Add 250 ml (about 1 cup) of water into a glass container or some other vessel that can stand boiling water. The container should be something you can cover. Glass bottles that can stand boiling or canning jars work well.
  2. To this add 15 grams, about 1 tablespoon of instant chicken broth crystals. and stir until dissolved. Cover loosely so that steam can escape, but dust and dirt cannot enter.
  3. Microwave the broth on high for 3 minutes or until it just begins to boil.
  4. Let the broth cool and sit for at least 2 hours up to overnight at room temperature. Make sure that the medium vessel is covered to prevent contamination from the air. At this point the vegetative cells are dead and most endospores will germinate.
  5. Repeat steps 3 and 4 a second time. This will kill the endospores that germinated on day 1.
  6. Repeat steps 3 and 4 a third time. This will eliminate the remaining endospores, making the medium sterile.
  7. Place the medium in a warm place overnight. If your tyndalization was done correctly, your medium should remain clear and free of microbes.
  8. While you are waiting for your medium, search for a sample you would like to inoculate into it. Almost any sample should work, but natural samples are a good idea for this experiment. Samples coming from food or from your body may contain pathogens. Something you probably want to avoid.
  9. Check your medium. If it is still clear and sterile, add a pinch of your collected sample to the medium. (The exact amount really does not matter). Again place the medium in a warm place and check it periodically. After a few days, you should start to see the medium become more turbid.
  10. If you have the equipment, examine a sample of the medium under a microscope. What shapes of microbes are present? Is there more than one species?
  11. When finished, carefully dispose of the borth. It is basically a spoiled food, but the properties of the spoilage microbe are unknown and should be treated with care.
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