Ask your questions about bacteria and other microbes

Dr Clare Taylor, a Senior Lecturer in Medical Microbiology at Edinburgh Napier University, and also General Secretary of the Society for Applied Microbiology joined us for a live chat about micro-organisms – just how dirty are tea towels? What can we test? And how dangerous (or safe) are bacteria in your child’s nappy? Clare’s research is broadly based on infection control, and looks at different ways of eliminating harmful bacteria from different environments, as alternatives to antibiotics. While waiting for everyone to join, Clare was asked to introduce herself and the work she does.

Clare: I would call myself a molecular microbiologist because I am interested in understanding how bacteria works at the genetic level, i.e. which genes cause what, but I have done lots of different types of microbiology ranging from hospital infections to Salmonella, to understanding how bacteria gets into the food, and of course, have a general interest in how bacteria interacts  with our bodies.

Kate: The reason I’m excited is one of the most compelling things that we’ve found, is what was in our 5 nappies needing  to be ‘strip washed’ that we had analysed by Shirley Technologies. The perception has been for a long time that nappies suffer from a build up of detergent, and that causes them to smell and perform less well. However the nappies we had analysed didn’t seem to have a detergent problem. They did seem to have a bacteria problem though (and 2 had a build up of hydroxyl apatite). Now the burning question is how much bacteria is OK. Do you think we could quantify in any useful way how much bacteria in a nappy is OK? It would help give us a context for the results of some of our other tests too.

Clare: See this is the thing about bacteria, and how much is OK is an important question! Also it is important for us to understand which bacteria are present. Poo is mainly made up of bacteria that we find in the gut which get excreted along with other waste that we can’t digest. None of these are normally harmful so I guess the amount isn’t an issue in terms of infection. However it is bacteria that are still present in our laundered clothes that cause things to smell a bit musty sometimes.

Chantelle: Some other tests the group has done identified both g+ and g- bacteria on the nappies in many cases. Can you explain the difference?

Clare: So Gram+ and Gram- is a way in which we can classify bacteria into 2 main groups based on the structure of their cell walls. Gram+ have thick cell walls which protect them from the environment. Gram- have thinner walls but have a slightly different structure. The whole Gram+ or – is essentially based on the thickness and whether bacteria stain pink (Gram-) or purple (gram+) in a test that we can do.

Kate: When you say poo is mainly made up of bacteria from the gut, do you mean the bacteria in poo is mainly that type, or in a recipe for poo, bacteria would be the number one ingredient?

Clare: In a recipe for poo, bacteria would definitely be the main ingredient – I think they make up something like 2/3 of faecal mass! Bacteria in our poo are not normally harmful!

Kate: Amazing!

Chantelle: Great explanation. Which kind is the gut normally made up of? These are kind of leading questions because in the report some of the bacteria was labelled as normal gut bacteria and others as ‘potentially harmful’.

Clare: Bacteria like E. Coli, for example, are Gram- because they have the thin cell wall but bacteria like Staphylococcus are Gram+. We can find both of these types of bacteria in our guts and also in our poo!

Kate: So with their thicker cell walls are Gram+ bacteria more likely to hang around and be difficult to wash away? Consequently more of a risk to health?

Clare: The gut bacteria are with us all of the time and are mostly our friends. Sometimes if we get really stressed, conditions in our bodies can change and some bacteria can take advantage of this. Our bacteria grow in finely tuned conditions, and anything that upsets them can cause an imbalance. Sometime this can mean that a bacterium can cause what we call an opportunistic infection, or it may leave us susceptible to a new infection.

Chantelle: It’s mostly dead bacteria leaving the body right?

Clare: Some of them will be dead, but some of them will be live and kicking so to say!

Kate: I’m also interested in how we wash them away, just thinking of them as soiling in our clothes and separately from whether they are a health risk?

Clare: The chemicals in detergents help to remove bacteria. So going back to Gram-/+ for a minute some of the chemicals you get in detergents dissolve the Gram- cell walls really readily, less so with the Gram+ which are more difficult to get rid of.  A combination of different chemicals and heat will reduce bacterial numbers.

Chantelle: Does every poo contain bacteria other than normal faecal bacteria or potentially harmful bacteria e.g. E. Coli or staph with it?

Clare: Poo contains E. Coli bacteria for sure – most of us have it in our guts. but not the nasty harmful E. Coli that has killed people – you get that one from contaminated food.

Kate: Can I just clarify can a normally harmless poo dwelling bacterium cause problems if there is a vulnerability? I guess I’m trying to get at whether we need to be looking at specific types or if general bacteria count is the most useful indicator?

Clare: So do any of you take probiotics? Because probiotics are basically made from bacteria isolated from poo!

Kate: Excellent!

Chantelle: So gram+ staph for example are harder to get rid of because of the thicker walls?

Clare: It’s impossible to remove all bacteria from anything we launder because the water we use is also full of bacteria. However we significantly reduce the number. Of course in nappies the number of bacteria present is likely higher than the number of bacteria you would find on a T-shirt.

Kate: That’s very useful. We’ve learned a fair bit about oxygen activated bleach in combination with bleach activators generating peracetic acid which we understand to be a good disinfectant. I guess that’s what’s breaking down those cell walls. We understand that agitation and water changes and heat are important too.

Clare: Bleach is amazing at killing bacteria because it reacts with oxygen which produces really toxic chemicals which really go for the bacteria!

Chantelle: The problem with bleach is the scare factor and also that it wears clothes prematurely. We are washing these things regularly and vigorously. In the US people are more commonly using bleach on clothing but I find that in Europe it’s taboo almost.

Kate: I think it seems to depends on the branding too. In some  people’s minds mainstream detergent with bleach = harsh, but nappy detergent with more bleach = gentle.

Kate: Is it possible to say what sort of substance bacterial cell walls are made of? Proteins?

Clare: Bacterial cell walls are made up of fats, sugars and proteins. Different types of sugar molecules are joined together which give the structure, and these are interspersed with fats and proteins.

Chantelle: Is there some kind of standard number of what is normal, even on a t-shirt? We don’t live in a sterile environment but at what point is it too much bacteria?

Clare: There isn’t a standard number that I am aware of in clothes – and probably impossible to estimate. Depends on individual types of material, temperature humidity – all sorts of things! Our food isn’t sterile and we ingest that directly. In fact food will contain some of the nasty bacteria we worry about, like Salmonella, but we know that they’ll be destroyed by cooking and stomach acid.

Kate: Is it at the point where we can smell it, or before that we get to too much bacteria I wonder?

Chantelle: I think it’s arbitrary and depends on the type of bacteria and the person. Potentially even one live bacteria could cause an infection if the person’s immune system isn’t up to scratch

Kate: I wonder then if lipase, amylase and protease in a biological detergent formula actually act directly on bacteria too?

Chantelle: Great question from Kate about enzymes. In addition to that are the surfactants in detergent pulling off the bacteria from the laundry? If so does it kill them in the process or just wash them away?

Clare: Yes, the enzymes are the best thing at helping to remove the bacteria!  I’ll let you into a secret.. Before I heard about NSG we had always used non-bio washing powder. After I had looked at what you were doing I realised that it was because of non-bio that my jeans smelt a bit fusty… So I switched to bio and that got rid of the smell. Presumably because of the enzymes helping to get rid of the bacteria!

Kate: that’s a very useful thing indeed to know about enzymes!

Sophia: Ha-ha, even more impact!

Hannah: Can I extend the question to tea towels? Presumably a lot applies (except poo hopefully). We found some interesting stuff about temperature on washing nappies but should I be washing tea towels at 90? Or 60? Are they full of more hardy bacteria?

Sophia: I’d like to ask Hannah’s question about dishcloths too. And flannels.

Clare: Dishcloths and tea towels will also be full of bacteria. But they won’t usually cause any problem. Apart from the smell! Because the smell is caused by bacteria breaking down compounds on the cloth. The same with body odour – cause by bacteria breaking down chemicals in sweat!  I guess what I am trying to say is that unless there are nasty bacteria in nappies/ laundry/tea towels etc (and there won’t usually be) it’s not a problem, in terms of risk of infection.

Kate: So the little bacteria are eating up the traces of food on our dishcloths?

Clare: Yes that’s exactly it! The bacteria are breaking down the traces of food so they can get their own nutrients!

Chantelle: What about picking up bacteria from the environment? Studies show that kitchen sinks and floors are teeming with bacteria.

Clare: Yes, the environment is covered in bacteria – as are we! On our hands, hair, clothes – literally everywhere! However we are not normally bothered by them!

Chantelle: When I did bacteria tests on my nappies I used old tea towels to bulk up the loads. I did a boil wash before starting and took a control. after the boil wash the towels were still full of bacteria. After washing, even with good detergent, the towel bacteria was still there, much more than the bacteria that was coming from the poo slurry I used. The bacteria grew differently and was easy to identify as being separate from the poo bacteria.

Kate: I have one more question about bacteria ingredients and enzymes. I read (but couldn’t access to the book that was cited), that some bacteria use cellulose to build their biofilms and that made me wonder if cellulase is also a useful enzyme for attacking bacteria?

Clare: I guess bacteria could use cellulose as a structural scaffold. Bacteria that we find in humans can’t normally digest cellulose but they can probably stick to it and then build biofilms on it. So if you remove cellulose you probably do remove some biofilm.

Chantelle: I guess what concerns me is that the bacteria was so hardy and hard to kill. Could it most likely be non-harmful? Because now I wash my tea towels more thoroughly than my nappies!

Clare: I wonder if that is something to do with the fact that they were older tea towels? It might be that the bacteria had gained a foothold so to speak because they had broken down the fibres and penetrated further.

Chantelle: So in general then the same procedure applies for tea towels? If they smell ok after one solid wash on 60 then they are good to go? I autoclaved and bleached the hell out of them after the testing.

Clare: Your tea towels sound like they must be the cleanest in the world!

Chantelle: Well they start out totally disgusting. We pretty much use them for everything rather than paper towels. And I use a lot until I have a full load. But there are studies showing that there is a lot of potentially harmful bacteria in the kitchen. So I have to imagine that the towels pick that up and can start to culture the bad stuff in the few days between washing.

Kate: Bit of quiz knowledge that seems pertinent. On the remote island of St Kilda off Scotland people lived in stone houses. There was a shortage of soil on the rocky island for growing veg so they would tramp the fire ashes food waste and animal waste into the floors of their houses throughout the year until it was two foot deep. Then they would dig that out and put it on the ground to grow more food in. They couldn’t have been more acquainted with their kitchen bacteria 🙂

Sophia: Does that mean that in older nappies the bacteria may have gained a foothold in the same way?

Chantelle: Great question.

Clare: I’m really interested in the phrase “”had broken down the fibres””.  Does bacteria damage the fibres of our clothes and nappies?”, so although bacteria that we find on nappies can’t digest cellulose directly (i.e. they don’t produce specific enzymes) it is possible that other by-products of bacterial growth could damage the fibres – so maybe when I said ‘break down’ that wasn’t quite the correct phrase,  but I do believe bacteria can certainly damage the fibres which might increase the surface area, and allow them more spaces to grow on. Does that make sense?

Kate: Yes it does. Bacteria can’t eat cellulose which might rough them up a bit and give them more surface to hang on to. The main purpose of cellulase enzyme as I understand it is to shave off the little bristles of damaged areas of fibres so that dirt has less of a chance of clinging on there (as well as looking less fuzzy) so it could also impede the bacterial growth a bit by the sounds of it.

Chantelle:  It could also be wear and tear from repeated washing that is breaking down the fibres and allowing more of a bacterial foothold.

Clare: Also true about repeated washing

Hannah: Fascinating stuff. Makes me feel a bit better about washing everything at 40 most of the time. When I was a kid I remember my Mum and Nan doing boil washes on the hob in a giant saucepan for nappies/dishcloths/tea towels. They still bleach dishcloths. I’ve always felt quite slack that I don’t.

Grace: Hi! Can I ask you to talk a bit about biofilms. Is it correct that they repel water and that they are difficult to remove ?

Kate: YES, that question.

Clare: There are thousands of researchers across the world trying to figure out how we get rid of biofilms! Biofilms are everywhere e.g. plaque is basically a biofilm in your mouth, that pink stuff that collects around the plug hole is also a biofilm (maybe just my sink…), and we know that different bacteria are found in different biofilms in different places.

Sophia: Can I ask how feasible would it be for us to do simple microbiology experiments at home? Like, could we send volunteers agar plates and get them swabbing their tea towels? Or is there some reason we shouldn’t do that?

Clare: I’m sure we could do something to look at tea towels at home!

Kate: Do you think a fabric with a very healthy biofilm could repel liquid?

Grace: We have seen poorly performing nappies with biofilms. We surmise the biofilm is the culprit in reducing the function. If they are implicated how do they form?

Clare: Biofilms are more resistant to all sorts of things – chemical disinfectants, antibiotics but I’m not sure that they all repel water – I think a really mature biofilm such as you might find on the inside of a pipe is impenetrable but doesn’t repel…. It might be that if some nappies are made of materials where a biofilm is more likely to form, then some of the bacteria are protected because the detergents etc can’t penetrate. That’s actually a tough one to answer!

Sophia: What are the biofilm a made of other than bacteria? I mean what is sticking them together? (Sorry if you already covered that).

Kate: Repel is maybe not a helpful word. Do you think water might struggle to soak into a fabric which had a mature biofilm on the outside?

Grace: If it is impenetrable and covers the entire working surface of the nappy then could it be impermeable i.e. the liquid cannot pass into the fibre structure?

Clare: Yes that’s more likely, but we would need to use an electron microscope (EM) to look at the biofilm to see if that was true.

Sophia: Or if the bacteria cover the surface of the fibre maybe they just make it a smoother shape giving less space for water to cling on to the fibre? (Does that make sense?).

Clare: Yes  that is a possibility about smoothing the surface.

Kate: Would you expect a synthetic fabric like polyester to be different to a cellulosic fibre like cotton in terms of how easy it is for a biofilm to get established there?

Clare: Yes – different fibres will have different properties and that will mean that the biofilms might be slightly different. So initially bacteria are attracted to a surface by its physical properties, such as surface charge. Once the bacteria get a foot hold they produce proteins and sugar-like molecules to produce a scaffold that holds the biofilm together! However it depends on which bacteria can interact with each other as to which bacteria end up in the biofilm!

Kate: Did we get to see any of the ‘repelling’ polyester nappy under the microscope?

Sophia: No, but we still have it.

Grace: (Clare) Have you got an electron microscope? We have some biofilm covered nappies we would love to loom at more closely.

Kate: That would be really interesting to look at it and see what is going on there. We know that cellulosic fibres truly absorb while synthetic microfibre ones more give liquid places to hang around and the shape of the microfibre is important in that. Maybe a biofilm like Sophia is describing  could be covering up the gaps in the microfibres which make it work?

Clare: I certainly have access to an EM and we could try and take a look. I can have a look to see how easy it would be to look at things under the EM. And I’m happy to explore how we could do some more bacterial testing.

Grace: That would be super awesome

Chantelle: Awesome!!

Kate: I’m desperate to see now! The charge thing is interesting too. I wonder if surface charge varies between synthetic and cellulosic , and I wonder if there are any implications with fabric softness produced, either with fabric softener,  or drying in the wind, or tumble drier, as that’s to do with charge too I think.

Clare: Yes, I expect all of that contributes!

Kate: The ‘repelling’ nappy was minky which is long pile polyester microfibre. Heavily dependent on surface area for holding water. I think it feels different when it’s not working right. Previously it’s been accused of holding on to oils but maybe it’s just bacteria.

Kate: Would cloth with a healthy biofilm feel different? And might it have a colour?

Clare: To be honest I’ve no idea how a biofilm would feel on cloth. Except that dirty cloths kind of go a bit slimy. Allegedly. Not my cloths obviously… 😉 As for colour I think you’d need a pretty heavy build up of biofilm for there to be colour!

Kate: Yes. Biofilms will have a feel but it might be the same feel as the cloth? Maybe! I’ll need to investigate this now! OK so it sounds like there’s a few projects brewing!

Sophia: If we could show that by looking at it with an EM then we would have solved one of the great mysteries of nappy world!

Kate: You can feel plaque on your teeth and that pink stuff in the bathroom (other people’s bathrooms and teeth obviously).

Clare: True but that’s on a solid non-absorbent  surface which has different properties.

Grace: Can you identify different bacteria under the EM like you can identify different elements? Or do we have to do more extraction based experiments to work out what bacteria is at play?

Clare: No the EM wouldn’t tell us what bacteria they were – we would only able to tell shape. We would have to do other tests to find out what they were.

Sophia:  Erin [an NSG volunteer who works in a lab] can get all the bacteria sequenced I think.

Chantelle: Could we devise a test to see how much dead bacteria remains on a nappy? In Denmark a lot of people like to use boil washes all the time to wash their nappies and I am concerned that this is going to only kill bacteria rather than remove it. They generally don’t use enough or strong enough detergent, and if they use anything with enzymes, the enzymes will be denatured at that temp anyway. I guess further to that is whether a large amount of dead bacteria could cause problems? It’s my understanding that dead bacteria is going to be a food source for living bacteria.

Clare: There are certain stains you can use to look at live/dead bacteria. I’ve only ever used them in terms of bacteria associated with live mammalian cells, maybe it could work on nappies. We’d have to investigate!

Kate: In any case if bacteria make up most of poo, and you’re just killing it and washing it back into the nappy that’s a fair amount of soiling whether it’s unsanitary or not.

Chantelle: Oh yes I’ve actually done some fluorescent staining on fibres. It worked ok but I think it would be best if we could somehow isolate whatever is left on the nappies from the fibres. The fibres seemed to also pick up some stain. Yes, but dead bacteria *should* be slightly easier to remove so maybe then the water and scrubbing are doing a decent job of things. Playing devil’s advocate now.

Chantelle: Isn’t live bacteria is more ‘sticky’ than dead bacteria in that it is actively working to stay attached to the surface?

Clare: It’s interesting I’ve never really thought about remnants of dead bacteria before but yes they would provide nutrients to living bacteria.  Yes, live bacteria would definitely be more sticky than dead ones. Dead ones only would likely have burst open.

Laura: Burst open bacteria…that’ s my nightmares for tonight sorted.

Clare: You have to think of bacteria like soup in a bag. If you burst the bag the contents leak out!

Chantelle: mmm bacteria soup!

Clare: Don’t worry – the contents are usually harmless. Unless it’s something like Anthrax! Then you’d be in trouble anyway!

Grace: Also if the biofilm is impermeable, the dead bacteria could be falling out of the film but still be trapped under it within the fibres, and feeding the live bacteria. Is that a correct statement?

Clare: Yes that is true – dead bacteria would remain trapped in the biofilm.

Chantelle: I am an hour ahead so have to get to sleep now but happy to talk more and help devise some kind of experiments. I think trying to figure out live/dead could be critical here since many are using either heat or oxygen bleach to kill bacteria but then may not be using enough surfactant/enzymes etc to remove it.

Clare: Excellent. Sophia has my email address so feel free to get in touch!

Kate: If there is any time left I just remembered a theory e.g. sunlight is harmful to bacteria. I’ve noticed that wetting and drying in the sun, then wetting and drying again increases the effect of bleaching stains. Might it increase the impact on bacteria?

Clare: UV basically denatures bacterial DNA so it is harmful to them. Same for us except that bacteria are smaller, so it has more of an effect! Argh. This has been so much fun! I don’t want to stop! But. Must. I’ll say goodbye and thank you all of for your superb questions! Sorry if I missed any! And it would be my pleasure to join you again! Night all!

2 thoughts on “Ask your questions about bacteria and other microbes

  1. Back to the tea towel question. I replace the tea towel in our staff kitchenette with a fresh tea towel daily. This kitchenette is serviced by around 24 staff who generally bring in precooked meals that are heated in the microwave, or make sandwich toasties as their is no stove or oven available to prepare a meal from scratch. The tea towel is only used to clean dishes, not people’s hands as their are paper hand towel available for this. Considering this scenario, what is the likelihood of this tea towel being germ ridden and how often should it be replaced to prevent staff potentially becoming sick as a result of using it?


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