Naked Science Forum
Life Sciences => Cells, Microbes & Viruses => Topic started by: Wilf James on 02/11/2011 17:01:02
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Wilf James asked the Naked Scientists:
Dear Chris,
There has recently been some discussion on the radio (4) about low temperature washing of clothes.
I gathered the impression that bacteria are not killed in a wash that takes place below 60 degrees C. There was no mention of what sort of washing powder or liquid is used. I currently do all my washing by hand with a biological wash powder bought from Lidl. It works well and is good at removing stains from underclothes at temperatures around 35-40 degrees C.
I had presumed that the enzymes in the wash powder would break down the proteins in the cell walls of bacteria, thus effectively sterilising the washed items. Please can you tell me if my presumption is likely to be correct?
If it isn't, there would be no point in using a biological wash powder because the enzymes decompose at temperatures above 40 degrees C, the temperatures advocated for making washed clothes sterile.
On a further point is domestic bleach containing sodium hypochlorite good at killing bacteria? The claims made for it (for a well known brad) say that it kills 99% of all known germs.
Your advice on this topic would be very welcome
Wilf James
What do you think?
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the enzymes used in washing powders are produced by bacteria. They might kill some bugs, but they certainly won't sterilise things. However, they will remove a lot of things like food or blood stains which would harbour bacteria.
Sodium hypochlorite is very good at killing bacteria. The ads used to say "kills all known germs" and they were right.
A high enough concentration of bleach for long enough will kill everything. However if the material is not clean then bugs can "hide" in the dirt and be protected from the bleach.
Another point to remember is that humans are able to live in environments that are a long way from sterile so there's not much point even trying to kill all the bugs in your clothes.
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No - in fact bleach will not kill "everything" in application. Bacteria in biofilm and fungal mass (esp melanized fungi) will maintain viablity after exposure to bleach.
Washing itself generally removes much of the bacteria as part of soil and a fair amount is redeposited. EPA has recognized laundry sanitizers and disinfectants and indicated specific methods for each.
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Why isn't there a layer of slime on the inside of the bleach bottle?
It takes a high concentration, and a long time, but bleach does kill bugs, even if they are hiding in a biofilm.
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The bugs have to establish the biofilm before they are protected. They'll not grow in bleach to estblish biofilm.
How long a long time is may be open for discussion but bleach does not penetrate biofilm well. I'm familiar with up to an hour exposure of heavy biofilm as well as mycelium of melanized fungi with some level of viabiity maintained. Dynamic wth biofilm is that highh pH of bleach as sold does dissolve some of the polysaccharide but precipitates protein component but it's most active in kllling at slightly acidic pH as hypochlorous acid. And bleach doesn't eliminate viability in form of bacterial endospores and some fungal spores and of prions (whatever life form we consider those to be).
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When did the Hoffman degradation stop working?
It's illustrated here
http://en.wikipedia.org/wiki/Hofmann_rearrangement
with hypobromite, but the hypochlorite wors too.
The point is that this reaction is general for amides.
Given time, it will degrade any amide.
All life (whether we include prions or not) will contain amides- the biologists call them proteins- but they chemistry is the same.
What life form can survive in an environment that destroys proteins?
At low concentrations of hypochlorite the bugs might be able to repair themselves by making new proteins as fast as the old ones are destroyed but I don't imagine that will happen in bleach.
Also, on a more practical note, how come I can clean the toilet bowl with bleach?
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Perhaps you might acquaint yourself with real life microbiology/microbiological soils. In that context, you need to apply mechanical disruption of biofilm with bleach to get it "clean" presuming you've not scale. But be my guest, you and Hoffman can add bleach and watch the biofilm not disappear.
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Unless you're immunosuppressed, washing your clothes is just fine. The bacteria on your clothes are more than likely normal skin flora and not going to hurt you anyway. You wash clothes to make them look better. There are some bacteria that will always make you sick, like Group A strep, but you'd probably get it from hand to mouth contact, not your clothes. Hospitals use disinfectsants and ultraviolet light to prevent the spread of drug resistant bacteria, but for the average person, that isnt a concern.
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I'm familiar with data indicating primary bacteria found in in the washing process are enterics. Do you have data re. skin flora being primary?
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"Perhaps you might acquaint yourself with real life microbiology/microbiological soils."
More real than cleaning the toilet?
"But be my guest, you and Hoffman can add bleach and watch the biofilm not disappear."
I'm not going to post "before and after" pictures, but I assure you that bleach really does clean the bowl. The fact that it's a soft water area and bleached regularly probably helps.
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Well yes, enterics would probably be found on clothes and other objects as well, but most of those are normal flora as well, and predominantly harmless, and in many respects helpful. Enterics or normal flora of the intestine digest plant material we are unable to, even produce a few vitamins, and they help keep out pathogenic or harmful bacteria from taking over the intestine by competing with them.
Clorox argument aside, I suspect most bacteria, at least the non-spore forming kind, wouldnt survive the heat and dryness of the clothes dryer.
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Clothes dryer heat was not part of the question - do washing powders kill bacteria.
But you are correct. Any risk would probably come with transfer of wet clothes to the dryer.
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Risk of
Clothes dryer heat was not part of the question - do washing powders kill bacteria.
But you are correct. Any risk would probably come with transfer of wet clothes to the dryer.
Risk of what? What are you afraid of or trying to prevent? You are sounding a little Howard Hughes-y. Unless you are immunosuppressed, the bacteria that might end up on your wet or dry clothes are not going to hurt you.
Most bacterial infections occur when a bacteria that normally lives happily and harmlessly in one part of your body (like your intestines) ends up in another apart of your body (like your urinary tract or your lungs) where it does not belong. Or a bacteria on the might be on the surface of skin and not causing any damage gets into a cut or surgical incision. There are a few outright pathogens, like say Group A streptococcus, that causes strep throat, or Neisseria gonorrhoeae, that causes an STD, but you are unlikely to get either from your clothes.
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I'm a microbiologist - you apparently are not. Risk means risk - whether small or large. I'm sure even you can think of a scenario of risk - and do spare me your amateur epidemiology.
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I'm not a microbiologist (though a few of my friends are).
On the other hand I am a Union Safety Representative and I work for an organisation that worries about risk a lot.
So I know enough about risk to say with some certainty that, in order to talk about risk, you need to say what risk you are talking about.
So, perhaps, rather than stating credentials that don't apply to the question in hand (i.e. risk analysis), perhaps you should answer the question.
Risk of what?
It's a valid question and there are certainly plenty of possible risks to consider.
your statement "Any risk would probably come with transfer of wet clothes to the dryer." could apply to electric shock from a poorly wired washer or to the risk of slipping on a wet floor.
Even if we just stick to microbiological hazards there are still a number of possible risks.
Obvious ones include:
risk of infection of any open cuts or grazes on the skin.
risk of contaminating the dryer
risk of aerosolising any bacteria that are present on the wet clothes
and plenty of others.
However I can state quite categorically that in my case there is no risk from transferring wet clothes to the dryer. I have a combined washer / dryer, so there is no transfer. You see it really is important to say what risk you are talking about.
So, as I said.
Answer the question
What risk?
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I'm a microbiologist - you apparently are not. Risk means risk - whether small or large. I'm sure even you can think of a scenario of risk - and do spare me your amateur epidemiology.
Actually, I worked as a microbiologist for 15 years and teach anatomy and physiology now. Yes, I do understand sterile technique. I just don't think it's necessary for laundry in the average home. Risk is relative, we take risks every minute of every day, and you do a kind of cost/ benefit analysis to see what level of risk you can tolerate to maintain a reasonable quality of life.
p.s. If you really are a microbiologist, and you are worried about bringing home pathogens from work, then there is something wrong with your equipment or procedures in your lab, and you are probably endangering people in the entire building, in which case you have a much bigger problem on your hands than what laundry detergent you should use. One solves these problems where they originate, not somewhere downthe line.
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I didn't know Howard Hughes was an adjective, but I like it [:D]
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You should have learned rik assessment in your 15 years. No sure the relvance of your claim of "sterile" (most microbiologists refer to it as aseptic) technique.
p.s - Please pay attention. I did't recommend laundry disinfection in the home. However, products exist for this specific application. The methodology derives from hospital applications (http://www.epa.gov/oppad001/dis_tss_docs/dis-13.htm).
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You should have learned rik assessment in your 15 years. No sure the relvance of your claim of "sterile" (most microbiologists refer to it as aseptic) technique.
p.s - Please pay attention. I did't recommend laundry disinfection in the home. However, products exist for this specific application. The methodology derives from hospital applications (http://www.epa.gov/oppad001/dis_tss_docs/dis-13.htm).
Please pay attention yourself, both to your typing, and to the fact that you need to explain what risk you are talking about.
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Mod note!
Everyone - Can we be a little less catty and snarky (C) in this thread? Thanks
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Fair enough.
Can I ask why the page about sanitising cleaners which Phil cites says this "The data requirements outlined herein do not apply to sodium-calcium hypochlorites, sodium-potassium dichloro-s-triazinetriones or trlchloro-s-triazinetrione"
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Would my comment about Howard Hughes fall into the "catty", or the "snarky", category?
(Come to think of it, "Catty and Snarky" sounds like a pretty good name for a cartoon series. I better nip down to the trademark office and register it before Matt shrinks this post.)
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Would my comment about Howard Hughes fall into the "catty", or the "snarky", category?
(Come to think of it, "Catty and Snarky" sounds like a pretty good name for a cartoon series. I better nip down to the trademark office and register it before Matt shrinks this post.)
Please note amended post above - I think name, date and sign are all that are required. :-)
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Sure bored - the risk is that contaminated laundry may act as a fomite carrying viable pathogens in numbers sufficient to cause disease from a contaminated source to a susceptible individual exposed to laundry during or after laundry process - per old story think smallpox/blankets/indians. Risk assessment would consider pathogenicity, infectious dose, mitigation (disinfection, dilution/heat in washing), susceptibility of hosts, etc. High risk would be for example Clostridium difficile in hospital and nursing home operations. In modern households, risk would probably be episodic and low. In US, products are marketed to both scenarios and in both must satisfy EPA criteria and registration.
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So, you say "Any risk would probably come with transfer of wet clothes to the dryer.".
Now I know that ordinary washing won't sterilise things, but it does remove gross dirt. That's what it's for.
And In another thread you have pointed out that many bugs will be unaffected by sunlight because they are hiding in this same dirt - and that's clearly true.
So it's clear that removing that dirt removes a lot of bugs.
You also rightly point out that washing is an important mitigating factor.
So surely the clothing poses more of a risk when you put it into the wash, rather than when you take it out?
In other words, your assertion was not only poorly constructed but plainly wrong.
Is that why it took you so long to reply to the question Cheryl asked?
Incidentally, how long do you plan to wait before answering my question about hypochlorite?
BTW, you really need to give up sending rude personal messages- they don't contribute a lot to the world.