How Clean Are Your Hands?


This exercise will be graded out of 30 points.

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Purpose:

To determine the amount and kinds of microorganisms growing on your hands.


Hypothesis:

Answer the following questions concerning your initial assumptions in a discussion entry.
  1. How much growth do you expect to find from your hand print? Why? (2 points)
  2. How many different kinds of microorganisms do you think are currently residing on your hands? Why? (2 points)


Materials:

  • 1-15mm x 150mm Brain Heart Infusion (BHI) Agar or Tryptic Soy Agar (TSA) plate per student
  • 1-3ml sterile water in 13 mm test tube per student
  • 1-Fine point Permanent Marker per student
  • Colored pencils
  • Gloves

Methods:

  1. Store agar plates upside down (or lid-side down) when not in use. Label the plate around the outside edge. Be sure to include your initials, the type of medium being used (BHI Agar or TSA Agar), the date, and the incubation temperature.
  2. Flip the plate right-side up. Remove the lid. Make a hand print on the agar, using caution so as to not poke through the soft agar.
  3. Replace lid and store the plate upside down in the 37°C incubator overnight. (Note: If a 37°C incubator is not available, plates can be stored at room temperature).


Results:

To be answered in your lab notebook.
  1. Draw the distribution of colonies from your hand print using colored pencils. (5 points)
  2. Observe two well-isolated colonies and identify the colony size, elevation, margin and pigmentation. Record your observations in a chart like the one shown below. (Each space worth 2 point for a total of 10 points).

Colony #1
Colony #2
Size:


Elevation:


Margin:


Consistency:


Pigmentation:


Conclusions:




Draw conclusions using the following questions as a guideline in a discussion entry.
  1. Comment on the amount of growth that you observed from your hand print. (2 points)
  2. Comment on the different kinds of growth that you observed from your hand print. (2 points)
  3. Did your observations agree with your expectations? Why or why not? (3 points)
  4. What conclusions can you make about the total number and diversity of bacteria found on your hands? (4 points)


May be reproduced for classroom use. Adapted from an experiment designed by Laura E. Duwel, Ph.D. © 2008 Jennifer L. Hillemann