How Good Is Your Toilet Paper

How good is your toilet paper

The purpose of this practical is:

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

aLabel the bases of three sterile malt agar plates with your name, the date and A, B or C.

bWash your hands thoroughly using hot water and soap, then dry them on a clean paper towel.

cOpen one lawn plate of yeast (Saccharomyces cerevisiae). Wipe the surface lightly with two fingers.

dLift the lid of dish A. Touch the agar surface lightly with the same two fingers. Quickly replace the lid.

eWash your hands thoroughly again.

fWrap your two fingers with one layer of one kind of toilet paper.

gOpen another lawn plate of yeast. Wipe your fingers over the surface – trying to wipe them in the same way as before.

hRemove the toilet paper and put it straight into the autoclave bag provided.

iLift the lid of dish B. Touch the agar surface lightly and quickly replace the lid.

jWash your hands thoroughly again.

kWrap 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.

lTape the lid on the agar plate and give it to your teacher to incubate inverted for 2-3 days at room temperature (20-25ºC).

mExamine the agar plate without opening it.

QUESTIONS

1What are you expecting to see on your agar plates?

2What do you think about the different kinds of toilet paper tested by your class?

3Do you always wash your hands after using the lavatory?

4Do your agar plates match your predictions?

5Has every group got the same result?

6If there are differences, are you confident they are because of the different toilet papers?

7From your class results, are some toilet papers better than others? Are some soaps better than others?

8Imagine 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?

ANSWERS

1Hopefully 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).

2Depends on student opinion.

3Do they?

4Depends on predictions.

5Probably some variation – depending on thickness of toilet paper and firmness of wiping technique!

6There are lots of variables in this protocol. Wiping technique and hand-washing technique could be very different.

7Depends on class results.

8Improve 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.