How many bacteria live on your hands?

What was growing on the hands of the Naked Scientists? And how effective is hand washing at dislodging these microbial passengers?
02 March 2015

Interview with 

Dr Michael Nicoll, University of Cambridge and Rachel Thaxter, Addebrooke's Hospital


Finger swabs from a Naked Scientist!


A recent survey of commuters' hands showed that up to 60% of travelers have faecal bacteria on their fingers. Women, administrators and people who travel by bus emerged as the worst culprits. You might hope that your doctor would have cleaner hands - and these days handwashing is a major priority - but it Hand bacteriawasn't always like that. In fact, it took the Hungarian doctor Ignaz Semmelweiss in the 1840s to make the link between doctors doing post mortems in the morning - without washing their hands afterwards - and a big surge in patient mortality in the afternoon!

But how effective is hand-washing, and what's living on our mits anyway? Chris Smith spoke with Michael Nicholl, a virologist at Cambridge University, and Rachel Thaxter, an infection control,nurse at Addenbrooke's Hospital...

Chris - So, you have brought along some Petri dishes, a fetching green colour and they have some red stuff and some dots. Tell us more.

Mike - So, because we don't want to recreate the experiment that Ignaz Semmelweis carried out, today, we're going to do a couple of demonstrations of the bacteria that live on the hands of the Naked Scientists' interns.

Chris - Tell us what you did to create those plates.

Mike - So, these are blood agar plates and they form like a food layer for the bacteria to grow on. What we did is we went and got the hands of the Naked Scientists, put them on the plates before hand washing and then one of them washed their hands and put it on the plate again, and the second person washed their hands but with an alcohol rub, like the stuff that you find in hospitals.

Chris - So, we're looking to see if standard hand washing versus alcohol based hand rubs would make a difference to the levels of bacteria because those little dots we're seeing, all kinds of nice colours and things growing on the plates, those are colonies of bacteria.

Mike - We have bacteria like everywhere on our bodies anyway, but throughout the day, we also pickup various other nasties. So, what we have here are the hands before they were washed, very nice plate here. You can see exactly where the three fingers of the intern were scraped across the plate.

Chris - So, what are those bugs?

Mike - These are very likely to be species of Streptococcus and Staphylococcus which live on our skin normally. Staphylococcus aureus is related to MRSA. Streptococcus is used in yogurt quite a lot and certain strains such as Streptococcus pyogenes are likely the cause of the disease on the ward that Ignaz Semmelweis actually treated.

Chris - So, the doctors doing the post mortem would've chopped up somebody who had died with this infection and got the bugs in increased numbers on their skin. When they went to see the patients in the afternoon, then they would've infected them with those microorganisms causing more customers for the post mortem room the next day.

Mike - Absolutely. It was interesting because the reason the thought occurred to him that there was an autopsy link was a friend of his was accidentally cut himself with a scalpel during an autopsy. He developed septicaemia, an infection of the blood. When he did the autopsy on his friend who dies as a result, he noticed that the lesions on his friend were the same as these women in the maternity ward. And so, he thought something is happening. Something is being transferred from the bodies, the decomposing bodies of the dead and being given to these women which is causing the disease. It was a huge breakthrough because at that time, people thought, to get sick, you got struck down by invisible poisonous gas called miasma. Which if you think invisible poisonous gas will hit you, there's no way of preventing that, you have no idea. So, people felt very powerless whereas when you actually control infection by hand washing which you did with the chlorine solution on the doctor's hands, you can actually say, "We can prevent disease being spread." There must be something more to it or something different of course than an invisible poisonous gas which will kill us.

Chris - And talking of hand washing, did it make a difference to our interns?

Mike - It did and they should wash their hands more often. When you look at the hand washing, you can see there's far fewer. There are still colonies on there but the job is pretty good. When you compare this plate here and compare it with the alcohol rub, you can see that this has killed most of the stuff that would live on hands.

Chris - Indeed. This plate which is from the hand after it's been cleansed with alcohol, that it's almost devoid of any kind of growth. It's almost sterile.

Mike - Absolutely. So, the alcohol will kill the bacteria that's sort of very much attached and colonising your hands anyway as part of your normal skin flora.

Chris - It seems extraordinary Mike, they must have seen these sorts of things growing. They must have seen for instance, bread going mouldy. So, how do people account for that then if they didn't have a theory or a concept of microorganisms?

Mike - People didn't know at all where it came from. In fact, most people thought that mould on bread was spontaneously generated. It would just come out of the ether. The experiments that we're talking about it occurred in the 1840s, but it would take about 20 to 30 years later for Lister to show that actually, when food is spoiled, or when wine is spoiled as he was doing, it was actually...

Chris - More important the wine, isn't it?

Mike - I mean, wine exactly. When the wine is spoiled, it's because the bacteria were falling into it and actually having a great time in the wine.

Chris - Thank you very much Mike Nicoll from Cambridge University. Because at the main stay of defending our health in hospital is good and immaculate hand washing, we thought we would invite one of the infection control team from Addenbrookes Hospital Rachel Thaxter to come and give us a lesson and also, show us how good or bad we are it.  Please welcome Rachel Thaxter. So Rachel, you're on the war path after any doctors and nurses who don't wash their hands properly. How much of a difference does it really make? I mean, we've seen some plates here with some cultures on, but are they the kinds of bugs that really make a difference?

Rachel - They are certainly, yeah. As Mike said, Staphylococcus, Streptococcus, we have these things on us and they do cause real problems in some patients. But it really is what you do with your hands that is the problem and your technique of washing your hands.

Chris - You've brought with you this thing. I love this. Glow and Tell. Tell us all about it.

Rachel - I'm going to ask a volunteer to come from the audience.

Chris - Let's welcome them up. What's your name?

Lucien - Lucien.

Rachel - I'm going to squirt this cream into your hand, I want you to rub it in like a hand cream and then have a look at your hands under the UV box and see how much you've got on your hands to make sure you've got good coverage. I want you to go to the bathroom and wash your hands like you would normally at home, then come back and we'll have a look at how you've done with the UV box.

Chris - Right. So we're putting them under the UV light and actually, you can see on Lucien's hands, it's glowing bright blue.

Rachel - Chris, I've got some on my hands as well. I shook your hand. Let's see how much you've actually got on your hand.

Chris - Right. so, I've literally just shaken hands with you. Look, all my fingers are glowing up actually.

Rachel - So, our volunteer has come back now. Let's see how they've got on. Not too bad actually Lucien. You just see. You're actually quite good at washing this hand here. You just missed a bit with your wrist there and your fingertips, I can see the very edge of your fingertips where your nails are. Are you right-handed Lucien?

Lucien - Yeah.

Rachel - So, you can see that actually you washed your left hand much better because your right hand is the dominant hand.

Chris - The bottom line is, there's still lots and lots of that dye. So, were those microorganisms that would be potential sites for transmission of infection. Rachel, thank you very much. Rachel Thaxter from Addenbrookes Hospital.


Add a comment