How good is your toilet paper
The purpose of this practical is:
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to find out how well toilet paper stops microbes getting on your hands
to show how important it is to wash your hands after using the lavatory
to find out if washing your hands makes a difference.
to see how pathogens can be transmitted
Procedure
SAFETY:
Do not open your plates when they are returned to you next lesson.
Investigation
a Label the bases of three sterile malt agar plates with your name, the date and A, B
or C.
b Wash your hands thoroughly using hot water and soap, then dry them on a clean
paper towel.
c Open one lawn plate of yeast (Saccharomyces cerevisiae). Wipe the surface lightly
with two fingers.
d Lift the lid of dish A. Touch the agar surface lightly with the same two fingers.
Quickly replace the lid.
e
f
g
Wash your hands thoroughly again.
Wrap your two fingers with one layer of one kind of toilet paper.
Open another lawn plate of yeast. Wipe your fingers over the surface – trying to
wipe them in the same way as before.
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h
i
j
k
Remove the toilet paper and put it straight into the autoclave bag provided.
Lift the lid of dish B. Touch the agar surface lightly and quickly replace the lid.
Wash your hands thoroughly again.
Wrap your fingers again in the same kind of toilet paper, wipe your wrapped fingers
on a third lawn plate of yeast, remove the toilet paper into the autoclave bag, wash
your hands thoroughly with the type of soap provided and THEN touch the
surface of dish C with your washed fingers.
l Tape the lid on the agar plate and give it to your teacher to incubate inverted for 2-3
days at room temperature (20-25ºC).
m Examine the agar plate without opening it.
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QUESTIONS
1
What are you expecting to see on your agar plates?
2
What do you think about the different kinds of toilet paper tested by your
class?
3
Do you always wash your hands after using the lavatory?
4
Do your agar plates match your predictions?
5
Has every group got the same result?
6
If there are differences, are you confident they are because of the different
toilet papers?
7
From your class results, are some toilet papers better than others? Are
some soaps better than others?
8
Imagine you are working for a toilet paper manufacturer to test toilet
papers, or working for a health promotion agency. Your investigation
would provide important information for your employer. How would you
improve this investigation to make the results more reliable? What would
you emphasise in your final report?
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ANSWERS
1
Hopefully they are expecting to see lots of yeast on plate A, very little on
plate B and very little on plate C. Colonies on plate B will tell something
about the efficacy of the toilet paper. Colonies on plate C will tell about the
effectiveness of hand-washing (if the toilet paper is not fully effective).
2
Depends on student opinion.
3
Do they?
4
Depends on predictions.
5
Probably some variation – depending on thickness of toilet paper and
firmness of wiping technique!
6
There are lots of variables in this protocol. Wiping technique and handwashing technique could be very different.
7
Depends on class results.
8
Improve it by mechanising – repeatable wiping technique, force etc. Also
using same thickness of paper each time. Improve reliability by repetition.
A health promotion agency will have different priorities from those of a
toilet paper manufacturer.
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