How clean are your hands?

Three weeks ago, when bread was still easy to buy, I set up an experiment to show my son what was on his hands and why he should wash them. We've already played with paint to show how germs spread and looked at how soap affects surface tension and why he should use it to wash his hands. These activities improved his hand washing and reduced his resistance to washing his hands, but he still sometimes had a wobble about it.

I wanted to try and make the invisible germs more visible and real to him. I've seen other people use bread for this purpose so I thought we could give it a go, the idea being that some of the germs (fungi/yeasts and bacteria) on his hands will grow on the bread as they can find the nutrients they need to multiply.

Putting his hand on the bread after he's washed it

I took three pieces of bread and he pressed his hand on two of them, one after playing in the garden and the other after washing his hands with warm water and soap. The third was our control i.e. one to see what would grow if he didn't touch it so we could deduce whether anything that grew must have come from his hands.

Complete set of samples

I was a little concerned about attempting microbiology at home and what we might grow from an unknown sample, so I took the following precautions:
- the small boy didn't touch the bread after he'd done the initial hand print, and I only removed the bread from the bag once at the end to take photos)
- we used his hand after playing in the garden so that we were likely to be growing fungi and bacteria found in soil
- I put the bread in plastic sandwich bags and folded the ends over. These would stop anything we were growing blowing around the house, but I deliberately didn't seal them tightly as I didn't want to encourage anaerobic bacteria to grow (these are the ones that can grow in your digestive system, away from air, some of which can make you ill).

Mould growth on the dirty hand sample and a little on the washed hands

It took a long time (about a fortnight) for there to be visible signs of growth on any of the bread. I suspect because commercially produced bread contains preservatives designed to inhibit mould growth and give it a longer shelf life. But eventually we got a nice result... 

Roughly hand-shaped patch of mould

The bread with the handprint from before washing grew a hand-shaped collection of blue/green mould. The bread with the hand print after washing grew one spot of mould, showing that his hand washing was pretty effective, but we could do better. The control sample without the hand print had no visible growth.

Despite the long time between starting this experiment and getting results, he was still interested, although he wasn't impressed with the 'germs' that had grown after he had washed his hands!  I keep reminding him of those horrible blue/green germs when he's showing any reluctance to wash his hands and it seems to do the trick, for now at least.

Just a note on viruses, one of which is the germ that we're currently most worried about, the coronavirus which causes Covid-19.  Viruses only replicate (multiply) inside living cells.  The bread doesn't contain living cells, so viruses won't grow on it as they need the 'machinery' inside the host cells.  Bacteria and fungi can grow with just a source of nutrients as they are themselves living cells so both of these can grow on the bread.  The visible growth that we saw seemed to be a sort of fungus (mould).