Name: ______________________________ Date: ___________ Hour:__________
Bacteria live on or in just about every material and environment on Earth from soil to water to air, and
from your house to arctic ice to volcanic vents. Each square centimeter of your skin averages about
100,000 bacteria. A single teaspoon of topsoil contains more than a billion (1,000,000,000) bacteria.
These bacteria that are found everywhere also reproduce very rapidly through binary fission. Under
optimal conditions, certain bacteria can divide as rapidly as once every 20 minutes.
The point of this exercise is to demonstrate that 1)bacteria may not be seen, but they can be found
everywhere and 2) the effects of washing hands with regular bar soap verses anti-bacterial soap on the
growth of bacteria. We will use a sterile nutrient agar plate as a food source for our organisms to grow.
Part A: Bacteria in the Environment
Here we will examine all of the various places that bacteria can be found. Get creative here and try to
find places that other pairs have not used to see if bacteria is present.
Procedure
1. Collect one nutrient agar plate per pair of students.
2. Collect four cotton swabs (Q-tips) per pair of students.
3. If the nutrient agar plate is not divided into four quadrants do so as indicated below. Also make
sure your name is on the plate.
4. Be creative and using one cotton swab, touch an area and then gently rub the swab over
Quadrant A. Throw this swab away.
5. Using a new swab, pick another area to swab for and rub this cotton swab over Quadrant B.
Throw this swab away. Do this two more times using the remaining two swabs and Quadrants C
and D.
6. Make sure to record each of the places that you swabbed and which quadrant you used. For
example, if you swab the door handle and put it in Quadrant A, write Quadrant A = Door handle
7. Turn the plates into the teacher.
8. After 24-48 hours observe your plates for growth.
Part B: Regular Soap vs. Antibacterial Soap and Bacterial Growth
Due to advances in science and technology we have become aware of some of the harmful effects
bacteria can have on humans. Because of this, steps have been taken to try and prevent some of these
harmful effects. One step that is useful in eliminating some harmful effects bacteria may have is the use
of hygiene, such as washing your hands. Today, there are many types of soaps on the market that are
labeled antibacterial, but the question is whether these soaps are any better than regular soaps.
In Part B, hypothesize whether there will be more bacterial growth on the antibacterial soap quadrant
or on the regular bar soap quadrant and then begin the procedure.
Procedure
1. Collect one nutrient agar plate per group of students.
2. If the plate is not already divided into quadrants, then do so like above. Also make sure your
name is on your plate.
3. One student in the group will touch Quadrant A, with unwashed hands, and the other student in
the pair will touch Quadrant B with unwashed hands.
4. Next, the student who touched Quadrant A, will wash his or her hands with regular soap, and
then touch Quadrant C.
5. Then, the student who touched Quadrant B, will wash his or her hands with antibacterial soap
and touch Quadrant D.
6. Put the top back on the plate and turn into the teacher.
7. After 24-48 hours, observe the plates for growth.
Questions Day One:
Complete these questions during day one of the exercise.
1. In part A, what areas did you swab for bacteria?
2. Out of these areas, which area do you think will have the most bacterial growth? Why?
3. In Part B, do you think that the Quadrants without the use of soap will have more or less growth
than the Quadrants that used soap? Why?
4. In Part B, do you think that there will be a difference in bacterial growth between the Quadrant
that used regular soap and the Quadrant that used antibacterial soap? If so, which Quadrant do
you think will have more growth? Why?
Follow-Up Questions
Complete these questions after you have observed your plates for growth.
1. In Part A, did you get any growth in your Quadrants? Which area that you swabbed, produced
the most growth? Why do you think that this area produced more growth?
2. In Part B, was your hypothesis correct? Did the type of soap seem to affect the bacterial
growth? Why do you think that this is?
3. From either part of this exercise, describe or draw some of the growth that you’ve see on your
plates.