Germs on my hands
November 16, 2009 2:17 PM   Subscribe

Is it possible for bacteria, and/or viruses to ever physically adapt to soap, alcohol, peroxide, iodine, ect.?

Washing your hands is the best way to cut down on a known vector for germs to spread. Could bacteria adapt physically in a similar way lice or hookworms have? Or does their size make it impossible? Same for viruses.

I know bacteria can and are adapting to chemical solutions like anti-bacterial soap. When hand washing with soap, the soap is not suppose to kill the bacteria, but it is the physical activity of rubbing that gets rid of the bacteria. The soap just makes it physically easier to transfer bacteria from your hands to the soap which is then washed down the drain.

As for viruses, could they ever evolve to the point that the usual disinfectants would not work? (alcohol, lysol, ect.)

Personal answers, opinions, anecdotes, are all welcomed, but links are always preferred.

As always thanks in advanced.
posted by MrMulan to Science & Nature (14 answers total) 3 users marked this as a favorite
I think the answer is most likely: see here or here or here....
posted by edgeways at 2:28 PM on November 16, 2009

regarding at least one type of virus
posted by edgeways at 2:30 PM on November 16, 2009

I can't quite tell if you're asking specifically about the potential for bacteria and viruses to develop resistance to those substances particularly when on the surfaces of the hands, or just in general.

Bacteria very commonly physically adapt to an environment in a way that makes them extremely resistant to insults like peroxide and antibiotics through the magic of biofilm formation. However, while biofilms naturally form in the mouth (in the form of dental plaque), they do not form on surfaces like one's hands.
posted by amelioration at 2:48 PM on November 16, 2009

There are limits to adaptation, of course, but they're remarkably high. In terms of acidic and alkaline environments, for example, there are bacteria that can withstand a pH as low as -.06 and as high as 13.

The book I linked, Life in the Universe: Expectations and Constraints lists many known limits of terrestrial life. Unsurprisingly, bacteria and archaeans beat eukaryotes in every category.

Of course, the downside (or upside, from our point of view), is that adapting to an extreme environment often causes the organism to lose its ability to compete effectively in more typical environments, so many organisms that can survive extreme environments are not effective pathogens.
posted by jedicus at 2:55 PM on November 16, 2009 [2 favorites]

There's a class of lifeforms (mostly bacteria) known as "extremophiles" who have been found living and prospering in environments previously thought to be utterly inimical to life. For instance, there are bacteria who live in the ground in the Yellowstone geysers, at temperatures previously thought to be sufficient to sterlize all life. There are bacteria who live in hyper-saline environments which should be lifeless. There are even bacteria who survive just fine when exposed to gamma radiation at levels previously thought to guarantee death.

Once field biologists took off their preconceptions and really started looking, they began to realize that there pretty much isn't anywhere on this planet's surface that's completely lifeless, except maybe lava lakes inside active volcanoes. They've even found bacteria living miles below the surface whose life process are so slow that they divide about once per century.

Given time, bacteria seem to be able to adapt to damned near anything.
posted by Chocolate Pickle at 3:10 PM on November 16, 2009

There's a class of lifeforms (mostly bacteria) known as "extremophiles"...

Most extremophiles are archaea.
posted by mr_roboto at 3:19 PM on November 16, 2009

The problem with hand sanitizers and the like, as far as bacteria goes, is the same as the problem with not taking all your prescribed antibiotics.

If you use anti-bacteria soap or hand sanitzers that claim to kill 99.9% of the germs, what are the 0.1% going to have in common? They're either lucky - or they are particularly hardy and live through the process.

Bacteria beget new bacteria - and in the case of your hands, they beget lil' fellas that are incrementally more resistant to alcohol or anti-bacterial agents.

Lather, rinse, repeat - and the result is the weakest are long dead while the strongest remain. Its why bacteria are awesome.
posted by neksys at 3:45 PM on November 16, 2009

More than you ever wanted to know about cleanliness.

In general, it is easier for an organism to adapt around a targeted chemical poison rather than a general physical principle or chemical bulk action (e.g. biocides). Examples of the first group include most antibiotics, since those only target one or two proteins which can either be mutated or lost without much loss of function. Examples of the second would be baking, autoclaving, UV or gamma irradiation, using bleach or peroxides, and lysol. For an organism to evolve around these constraints, it would have to change every protein it uses or evolve whole new compensatory mechanisms (e.g. Deinococcus radiodurans can survive gamma irradiation, but it's a fairly complicated resistance mechanism).

Note some viruses (e.g. rhinovirus) are already pretty hardy and aren't harmed by standard alcohol, lysol-type sterilizers, or UV. This is not a reaction to human activity, more likely the virus evolved to survive for long periods on hands in the sunlight between transmissions to a new host. This does not mean that HIV is likely in the next few million years to become a long-lived airborne virus.

There are plenty of extremophiles that are capable of growing in an autoclave, but that doesn't mean that the E. coli from someone's unwashed hands are going to become heat resistant overnight. It would take a very long time with a very long and slow gradient for a non-heat resistant bacteria to become a hot vent bacteria.
posted by benzenedream at 4:09 PM on November 16, 2009 [3 favorites]

Unsurprisingly, bacteria and archaeans beat eukaryotes in every category

I think yeast can have the highest osmotic tolerance...
posted by yoyo_nyc at 4:28 PM on November 16, 2009

Hand washing isn't any different from washing anything else. The soap simply helps to dissolve the dirt and make it easier to flush away with the rinse. So if the concern is a worry that some germs might adapt to become impervious to handwashing, it's not a big one. They might adapt, but they will do it in the drain, not on your hands.

Also, I can't cite the source, but I read somewhere that a bar of soap in the washroom often tests very high for bacteria...

But yes, bacteria can figure this stuff out. That's how they make different kinds of brewers yeast. Generations and generations of yeast are bred in successively inhospitable environments so that only the ones tolerant of the environment survive to reproduce.
posted by gjc at 4:35 PM on November 16, 2009

Alcohol-based hand sanitizers work by denaturing proteins and lysing bacterial cells. This can't be defended against in any simple way, like circumventing a certain biochemical pathway, in the case of antibiotics.

That's not to say that all microorganisms are completely vulnerable to alcohol. Some critters that have a spore stage are well-defended from things like alcohol and extreme temperatures.

In general, though, we don't have to worry about alcohol-resistance in the same way that we do antibiotic-resistance.
posted by chrisamiller at 4:42 PM on November 16, 2009

My recollection from somewhere is that one can breed bacteria (I forget which one was tested in this case — probably E. coli) that are able to withstand some physical mechanisms of killing them, like alcohol, but that there is usually a fitness tradeoff involved. The strain that was able to survive turned out to be an extremely poor competitor in conditions without physical assault, because it had to put a lot of energy into its membrane and not as much into dividing. Which is to say that it's unlikely that something that is hardy to alcohol or soap is actually going to be able to compete well in a world where there are still people who don't use those.
posted by Schismatic at 4:52 PM on November 16, 2009

In theory, I'm sure that a bacteria could evolve resistance against even things like alcohol, peroxides, soap, etc, but traits that allow an organism to survive with harsh extremes can also disadvantage the organism in less extreme conditions.

At the simplest level, it comes down to an energy budget. The more energy going into defense, the less energy available for reproduction. In the time between hand washings, a newly arrived bacteria without any soap resistance may have completely out-reproduced a population that managed to hang on through the last trip to the bathroom. Indeed, bacterial life is so competitive that just the added burden of duplicating the gene conferring soap resistance, quite apart from the cost of expressing the protein it coded for, could be enough to doom the strain in the absence of selective pressure from soap.
posted by Good Brain at 5:01 PM on November 16, 2009

How about spores? Several species of bacteria (notably those of the Bacillus genus) form an encased, 'suspended' animation lifestage that is not vulnerable to alcohols, or many other forms of disinfection, but the spores are also not growing while they are in this lifestage. And the predecessor of the spore (the mother cell) does make an investment in deciding to produce the spore rather than simply reproducing. Once conditions become favorable for the spores to leave the spore lifestage and become 'vegetative' again, the descendants of the spore are vulnerable to disinfectants in a way that the spore isn't.
posted by Tandem Affinity at 6:52 PM on November 16, 2009

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