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Biology 100


We share our environment with various and diverse microorganisms. Humans harbor various bacteria on their skin, in their upper respiratory tract, and in their alimentary canals. There are very few, if any, environments in nature in which bacteria do not exist. Bacteria have been isolated from such diverse environments as sulfur hot-springs associated with volcanic activity to super-cooled waters of the Antarctic.

This lab will consist of two parts. Each part will involve discussion and set-up during the first week and the reading of the results on the second week of the lab.

Part 1 Bacteria in our environment

You will identify some parts of your local environment you wish to test for the presence of bacteria.

Part 2 Effectiveness of hand washing

You will be conducting an experiment to test the effectiveness of various hand-washing methods and their effects on bacteria.


Part 1: Bacteria in our environment.

Work in groups of two.

Week 1

1. Decide what parts of your local environment you wish to sample for bacteria.

2. Obtain a sterile TSA (Trypticase soy agar) plate. Keep it sterile, do not open yet!

3. Label the bottom of the plate with the following: - students initials or names - type of exposure - date of exposure

4. Expose the plate. Do not open the plate longer than is necessary for your exposure.

5. Cover and turn upside down. Place on the tray provided for your class.

6. Let sit at room temperature until the next lab period. (The lab tech will check the condition of the cultures periodically. If growth is too rapid, the plates will be placed in a refrigerator to slow down the bacteria’s growth.) Week 2

1. Obtain your plates from the previous week and look at them for the density of the colonies and any diversity you can see. Diversity will be determined by differences in colony color, shape, size and texture. (Visual charts will be provided to assist with this). Each student’s information will be shared with the class.

2. Place all used plates in the bio-hazard disposal can. Do not throw in the trash can!

Part 2: Effectiveness of hand washing

The results for this experiment are gathered as a class. Each student will prepare one plate as assigned.

Week 1

The class will design this experiment including the following:

A. The 4 types of cleaning solutions to look at. Some examples could include: - water - plain soap - antibacterial soap - soap with a hand cream in it (dove) - alcohol

B. The amount and method of hand washing to be followed.


1. Obtain a TSA plate. Mark a cross on the bottom of the plate. Label the quadrants 1, 2, 3, and 4 respectively. Along the edge of the bottom put your initials, type of hand washing, and the date.

2. Lightly press your thumb onto the top of the agar over the area marked 1. Do not press too hard or you will put your thumb into the agar. It is a jelly consistency. Cover the plate right away. You do not want air-born contaminants to mess up your results.

3. Wash your hands in the manner decided by the class. Dry your hands. Press your thumb onto the agar over the part marked 2.

4. Repeat steps 3 and 4 pressing your thumb onto parts marked 3 and 4 respectively according to the procedures determined by the class.

5. Turn the covered plate upside down and place it on the tray provided for the class.

6. Let it sit at room temperature until the next lab period. (Again, the lab tech will monitor the bacterial growth.)

Week 2

1. Obtain your plate from the previous week and look at it for the density of the colonies and any diversity you can see. Diversity will be determined by differences in colony color, shape, size and texture. Compare the four quadrants. Was there a decrease in bacteria with increased washing?

2. Place all used plates in the bio-hazard disposal can. Do not throw in the trash can!


Each student will prepare an individual report on this lab using the combined class data. This report should follow the standard report format as presented in the introduction.

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