(2) Preparation of pure culture

      pure culture (single colony): 
          a population of cells arising from a single cell
  
    (A) Spread-plate technique

       Samples: 1. 0.1 ml tap water
                2. 0.1 ml drinking water from drinking fountain

      1. Pipette a small sample onto the center of LB agar plate.
      2. Dip a glass spreader into ethanol in a beaker.
      3. Briefly sterilize the spreader with flame and allow it to cool.
      4. Spread the sample gently and evenly over the agar surface with the spreader.
      5. Invert the plates and incubate at room temperature for 2 days.

   Homework:
     1. Count the number of colonies on each plate and figure out how many 
        microorganisms there are in each 1 ml original sample. 
        (Take a single colony as a single microorganism.)
  

 
    (B) Streak-plate technique
         
         samples:                suitable plates:
         yeast                   YPD
         unknown E.coli          LB, LB + ampicillin
         unknown microorganism   LB

     1. Briefly sterilize the inoculating loop with flame and allow it to 
        cool on a sterile plate.
     2. Dip the loop into microbial sample and streak the plates according to 
        the streaking pattern.
     3. Incubate at room temperature for 2 days.
  
   Homework:
      1. Describe the colony appearances on each plate. 
         Is there any pigment formation?
      2. Is the unknown E. coli ampicillin resistant?
      3. According to the appearances of yeast and E. coli that you have inoculated, 
         what is the unknown microorganism?