Measuring out precise masses of yeast for the hygiene experiment.
Mr John Di Mambro
Hutchesons' Grammar School
Dr Julie Rattray
Glasgow Caledonian University
Bhajneek Grewal, Nadia Hyder, Angel Lin and Zenub Qulsoom
'Wash your hands thoroughly after using the toilet!' is the advice of four students from Hutchesons' Grammar School, Glasgow. The students, all aged 17, spent the past year researching how easily bacteria can be passed from the human gut to hands after using the toilet. 'It is not commonly realised that toilet paper, no matter how thick or medicated, does not act as a physical barrier to the transfer of bacteria,' says John Di Mambro of the Department of Biology at Hutchesons'. 'The pupils' investigation showed that even several layers were not effective at preventing the skin picking up potential pathogens.'
Health and safety concerns prevented the pupils working with the headline hitting gut bacterium Escherichia coli 0157 - commonly known as E. coli. A neat alternative was found in Saccharomyces cerevisiae, a yeast commonly found on the skin and used in bread and alcohol production. 'Apart from safety, the yeast had the added bonus of being larger than E. coli which meant if it was transferable through toilet paper then the bacterium certainly would be,' explains John.
The pupils cultured yeast in broths and on agar plates allowing the production of countable colonies. After pressing their fingers onto the cultured yeast, the pupils then pressed them on top of a sterile plate separated by a variety of types and layers of toilet paper. Any yeast transferred to the sterile plate through the paper could be cultured and counted. The data on the transfer of yeast was linked to data on the spatial structure of different toilet papers as viewed under the microscope, and the thickness of the paper. 'Overall the results of the project were very revealing in terms of the difference between toilet paper brands, and also when using different numbers of layers,' explains John. 'Medicated papers did very poorly surprisingly and even the effect of colouring papers made a difference.'
To discover how people use toilet paper in terms of the number of layers of paper and frequency of hand washing, a survey of volunteer students was carried out anonymously. 'The questionnaire threw up interesting aspects of behaviour such as whether or not the toilet lid was closed before flushing to prevent aerosol carriage of gut contents,' says John.
To extend the project further, links were formed with Dr Julie Rattray a specialist in Microbiology at Glasgow Caledonian University. Julie helped the students consider possible extensions to their investigation and the significance of their findings.
'The project gave the students an opportunity to develop laboratory skills outside the normal school curriculum as well as the chance to present their findings through a variety of media,' concludes John. 'Flushed with their success these talented students have decided they are on a roll and won't be washing their hands of this project for a while!'