Thursday, October 25, 2007

Why Don't Bacteria Develop Immunity to Alcohol?

I've puzzled over this question for years, and can't find an answer. It is, no doubt, a stupid question, but waddaya gonna do? Maybe alcohol is just too damn efficient a killer for immunity to develop?


Blogger Random Michelle K said...

If I delve back years ago into my biology degree, my guess (and this is only an educated guess; my focus was on plants) is that the alcohol disrupts the water balance.

Cells have a delicate salt/water balance, and some substances can disrupt that balance by 1) causing water to flow into the cell, exploding the cell membrane or 2) causing the water to flow out of the cell, until the concentration of salt is too high and cellular functions are disrupted.

That's a really basic description of something I vaguely remember studying ... er ... awhile ago.

Hopefully that gives you a starting point for your researches, cuz I'm really supposed to be learning php/mysql right now. :)

4:28 PM  
Blogger The Mystic said...

Beeeeeeecause God made alcohol to kill bacteria?


5:13 PM  
Blogger Winston Smith said...

See, I guessed that alcohol must burst cell membranes or something...but...dumberer question coming...isn't that something that cells could also develop resistance to?

Maybe it's just harder to do so?

Anyway, thanks MK.

Check to see whether there are lead pipes in your house.

5:43 PM  
Anonymous Anonymous said...

Well, to take an example where I actually know something, there's quite a lot of variation in alcohol resistance between strains of yeast, which is how you brew very high alcohol non-distilled beverages I imagine that the reason that bacteria don't evolve of resistance to alcohol disinfectants is that they are used in very high concentrations and so you get pretty much complete bacterial death. You need differential reproduction to get evolution.

Oh, I should also mention that many disinfectants are isopropyl alcohol not ethyl, so it may (or may not) be harder to evolve resistance to isopropyl.

7:35 PM  
Blogger Random Michelle K said...

Because there are some things you just can't effectively build a resistance to.

Bacteria are as likely to develop resistance to alcohol as they are to high heat. Sure, it can happen (see: deep sea vents) but if a mutation appears for such resistance, chances are these bacteria will be out competed by "normal" bacteria, because they'll probably have a weakness in another area. Natural selection is not really all about "we'll build him bigger, faster, stronger", it's about who can adapt to survive specific conditions, and if those specific conditions are not consistent, run of the mill bacteria will out compete the specialized bacteria.)

If it helps, consider the fact that your body (inside and out) and most surfaces are covered by bacteria. However, the overwhelming majority of these bacteria are either benign or helpful (see: intestinal flora).
In most people, these healthy bacteria out compete the bacteria that make us ill. But sometimes the bad naughty bacteria get the upper hand, and then we get sick.

Regarding antibiotic resistance (which I am guessing is at the heart of this question), because hospitals are supposed to be sterile places, bacteria that have developed resistance to antibiotics can grow and thrive without competition from the normal healthy bacteria. So the hospital is really the last place you want to be when you're sick and have a suppressed immune system, because there are lots of horrible bacteria waiting to take advantage.

The other reason antibiotic resistance develops is overuse and abuse of antibiotics. When people who don't have a bacterial infection take antibiotics, or when people who do have an infection stop taking their medicine when they feel better without finishing the complete dosage, this encourages bacteria to develop resistance (i.e. what doesn't kill me makes me stronger). As these incidents increase, so do the numbers of bad bacteria that are resistant to antibiotics. (And where do people end up when they get sick and the antibiotic no longer works? The hospital.)

I actually know a lot more about antibiotic resistance from my public health classes than I remember of cellular function from my bio degree.

8:22 PM  
Blogger Winston Smith said...

THAT is a great answer, MK. I had wondered about the high heat analogy, but then thought of the volcanic vents...but did NOT think about competition with normal bacteria.

Super smart answer.

8:53 PM  
Blogger Random Michelle K said...

It's always good to put the results of my education to use--especially since I don't use any of it for my job!

Antibiotic resistance is a really fascinating thing--in a very frightening way.

Also, somewhat related, bacterial can go into dormant states and survive if conditions are *too* harsh. Which is why you are supposed to used diluted Clorox to clean, so you actually kill the bacteria instead of putting them into a hibernation from which they can wake up.

9:43 PM  
Blogger The Mystic said...

God made lead pipes cuz bald, insane people r hawt.

10:14 PM  
Blogger Tracie said...

According to my Microbiology text (I hate selling back textbooks after taking classes), alcohol is a lipid solvent and a protein denaturant. Basically, alcohols help dissolve cell membranes (and anything else with containing lipids, though the cell membrane is the most significant organelle I can think of) and unfold proteins, both really harmful things for any kind of cell.

Michelle, you're right on about everything (the dormant state you talked about is called an endospore -- which is almost completely indestructible and can remain infectious indefinitely.. I believe a TB endospore from an Egyptian mummy's tomb killed a few people when the tomb was opened). The competition answer is exactly correct. Since antibiotic resistance plasmids are energetically costly, regular bacteria can usually outcompete them. It's in human-created environments that resistant bacteria can thrive.

The same goes for alcohol resistant bacteria. A cell would have to expend an enormous amount of energy to develop a better resistant cell membrane/proteins to something that toxic. Additionally, some bacteria living in extreme environments aren't bacteria at all.. they're archaea, a lineage which split from bacteria a few billion years ago. They have some notable differences in their cellular structures so they can happily live in environments most organisms can't.

(Random note: It was from a thermophilic bacterium that the enzyme Taq polymerase was derived. Since the enzyme remains stable at high temperatures, it was perfect for PCR -- basically a DNA copy machine in which DNA is unwound using high heat, each strand is copied, the DNA is cooled (so there are two double stranded DNA molecules, both with an old strand and a new one), and then reheated and cooled to copy again exponentially. This invention lead to the enormous knowledge we have about DNA, genetics, and cellular mechanics today. The inventor is apparently a hippie in California who now spends all his time at the beach surfing.)

However, another thing I'd like to add as far as another contributing factor to antibiotic resistance is the fact that we put antibiotics like triclosan in *everything* -- soap, face wash, sanitizing wipes, baby toys.. the list goes on and on. Parents think that sterile = better for their kid, but in actuality they're not letting the kid's immune system work. This is thought to be the major reason why there are a ridiculous number of autoimmune disorders and allergies in children.

Plus, they're helping to create superbugs like MRSA, which has finally started getting the media attention it deserves. I remember reading an article in which a scientist or a doctor said that the number one disease he was worried about, as far as human lives were concerned, more so even than AIDS, was MRSA. Gotta be hard not to say "I told you so" now. I imagine many scientists are going to feel similarly when several low-lying cities are completely under water and animals like polar bears go completely extinct.

As far as antibiotic resistance goes, I think putting antibiotics in animal feed is an even worse problem than abusing antibiotics on ourselves, when you realize that it is routine to feed antibiotics to livestock even when they're not sick, and when you compare the number of animals to people. All in all, it's really amazing that we don't have more nasties like MRSA to contend with.

And yes, I am a Bio nerd.

1:19 AM  
Blogger Random Michelle K said...


I actually though about mentioning Taq and PCR (used to work in a microbiology lab) but thought it might be TMI. Glad you did it! (grin)

And antibiotics in animal feed are one of the reasons I only buy organic eggs, milk, and chicken (don't eat red meat). Unfortunately, the antibiotics are a requirement for cattle that are fed corn, since their systems can't property digest corn, and so it makes them sick.

Farming is really messed up in this country sometimes.

See, I can nerd right along with you!

8:50 AM  
Blogger Winston Smith said...

Thanks Traci, too!

Dueling bionerds = actual information...something we have way too little of around here...

The antibiotics in cattle feed drives me nuts. My uncle used to do that on the farm, but my dad put a stop to it when he took over.

A final question:
Is it very, very, very, very unlikely that bacteria will develop alcohol immunity (and still be able to compete with normal bacteria), or just, ya know, pretty unlikely?

10:06 AM  
Blogger Random Michelle K said...

How unlikely is it that bacteria will develop a resistance to alcohol?

Very very very unlikely unless people trying to sanitize everything and start wiping out good bacterial.

It's more likely than humans developing the ability to breathe underwater and taking to the seas to live. But not really all that likely.

All things are possible. Far fewer as probable.

3:47 PM  
Blogger Winston Smith said...

Again, very helpful. I hope you're right about that analogy--it puts my mind to rest.

Now I can go back to worrying about the Inevitable Zombie Apocalypse...

2:28 PM  
Blogger Random Michelle K said...



7:54 PM  
Anonymous Anonymous said...

A concentration of 70% isopropyl alcohol does destroy the bacteria so it is unable to develop resistance. It is like asking why humans do not develop resistance to bullets.

10:55 AM  

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