Name ___________________________
Bacteria I
The story of Bacteria
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Bacteria are a single celled organism that dates back over 3.5 billion years.
Bacteria are a prokaryotic cell
Prokaryotic cells, unlike eukaryotic cells found in animals and plants, lack a
nucleus, have no organelles and have a cell wall.
www.rst.gsfc.nasa.gov/Sect20/A12.html
Bacteria can help and hurt
Helping Bacteria
 There are over 100 trillion bacteria in your bowels that aid you:
1) synthesize half a dozen vitamins and help to supplement those
which are obtained from food
2) Convert dietary fiber--that part of food which humans cannot
digest--into small fatty acids which nourish the cells of the large
intestine
3) Degrade dietary toxins like methyl mercury making them less
harmful to the body
4) Crowd out pathogenic bacteria like Salmonella, decreasing the
risk of food poisoning.
 Some bacteria like actinomycetes, are used to make antibiotics
 Commonly found in dairy food products like in sour crème, cheese,
bread and yogurt
Hurting bacteria
 Known as pathogenic bacteria and it can cause disease or even death.
Name ___________________________
Bacteria is everywhere
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We will be looking at bacteria found on my hand washed and unwashed and a
pure culture of
 I will leave one media plates that as a class you will get to decide where to swab
and see what grows.
What are Plates?
What is Media?
What are colonies?
Staining Procedure
1) Place a drop of water on a microscope slide
2) Take the loop and sterile it under a flame and pick up some bacteria
off the Petri dish
3) Swirl the loop around in the water on the slide
4) Heat the slide to dry off the water
5) Add the Crystal Violet dye and let stand for about 60 seconds. Then
wash your slide with DI water. (The specimen should appear blueviolet when observed with the naked eye.)
Name ___________________________
6) Add Iodine (Mordant) stain and let stand for about 60 seconds. Then
wash
7) Add Ethanol (Decolorizer) until blue-violet color is no longer emitted
from the specimen. Then wash
8) Add Safranin dye (Counterstain) and wash
*Gram positive cells will incorporate little or no counterstain and will remain blueviolet in appearance because the crystal violet stain is held in once the mordant is
added and the alcohol dries the peptiodoglycan layer. Gram negative bacteria,
however, take on a pink color and are easily distinguishable from the Gram
positives. Things can go in and out of the lipopolysaccharide layer*
Name ___________________________
Bacteria in Yogurt
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Yogurt is simply milk, thickened to a custard consistency by certain acid-forming
bacteria growing in it.
The special bacteria that turn milk into yogurt are Lactobacillus bulgaricus and
Lactobacillus acidophilus and or Lactobacillus thermophillis.
The coagulation and the fermentation of milk sugar into lactic acid is caused by
these bacteria. This action curdles the protein in yogurt and acts as a preservative.
Now let’s see some Bacteria in yogurt
Procedure
1. Add 10 g of yogurt into a stomacher bag
2. Place 100ml of peptone water into the stomacher bag and mix by hand
3. Spread plate onto PCA (plate count agar) media
4. Incubate for 24 to 48 hours
Observations
Draw what you see in the microscope
Conclusion