FOOD                         Dilution            Total # of                 Bacteria per g or ml
                                              Counted            Colonies                   of Food Sampled

      _______________              _______             ________                   ________________

    (If 2 dishes between 30-300, use next line also)

      _______________              _______             ________                   ________________

QUESTIONS:
1. Consider each step of the dilution-pour plate procedure, and for the following indicate what kind of an
      error might be introduced into the final count:
      a. Example: pipetting - Possibility of an error in my reading the volume accurately or in the volume itself.

      b. Sample representation -

      c. Sample weighing -

      d. Dilution bottles -

      e. Counting plates –

2. Hamburger that is freshly ground under the best conditions often has a bacterial count of 1000 – 10,000
      per gram due to contamination. If your sample had 1,000,000 per gram, do you think this number of                  bacteria is due to contamination or to growth? Explain.

3. Calculate the number of bacteria per ml or g for the following sample plate count results. (SHOW MATH)
      a. Amount of food = 11 g | Dilution = 10-5 | # Colonies counted = 258 | # Bacteria = ____________

      b. Amount of food = 1 g | Dilution = 10-4 | # Colonies counted = 56 | # Bacteria = ____________

      c. Amount of food = 11 g | Dilution = 10-2 | # Colonies counted = 714 | # Bacteria = ____________

      d. Amount of food = 1 g | Dilution = 10-3 | # Colonies counted = 9 | # Bacteria = ____________