Originally posted by: Yossarian451
Think of it this way:
The antibiotic resistance is like a person slowly develping a resistance to a snake poison by injecting himself.
The alcohol is like a person trying to gain a resistance to his head being crushed by a sledgehammer by having someone hit him as hard as they can.
Sometimes you can survive the first one and then pass that on, you don't get to do that with the sledgehammer.
That's a very inaccurate analogy.
Antibiotics work on one (or a few) specific mechanism. They are highly active, so work effectively in very low concentration.
Because antibiotics work on one mechanism, and rely on their precise moelcular shape to block that mechanism effectively, any minor change in the molecular mechanism.
Essentially, imagine the biochmeical functions of a bacteria as a complex clockwork mechanism. The antibiotic is a precisely shaped key that can jam the mechanism. You only need one key, in the right place, to totally jam the mechanism. Resitance develops because a minor change in the mechanism stops the key from fitting.
Alternatively, you can get resistance due to a filter being put up around the mechanism through whcih the key can't go; dummy targets that soak up and destroy the antibiotic keys, etc.
Disinfectants are non-specific, they affect all biological processes, to a relatively small extent. They need to be delievered in high concentration (alcohol 70%, or bleach 10% solutions).
In the analogy above, imagine disinfectants are like syrup or molasses. They coat the whole mechanism, slowing it down (but not totally destroying it, unless they entirely flood it). There is no clever fit, so minor changes to the mechanism won't stop it from being jammed. It doesn't matter how many changes are made - the disinfectant will still work.
And, because the disinfectants are usually delivered at high concentration, there is little scope for bacteria to develop a system capable of filtering out the disinfectant.
So, in the case of antibiotics, a minor variation in the mechanism (which may in itself, be just a variant of equivalent performance, or even a minor disadvatage) can stop the 'key' from binding, and become a powerful selective advantage.
In the case of disinfectants, there is no single (or even small group) of changes that have a meaningful effect on sensitivity. So, little selective advantage through which resistance can develop.
Originally posted by: Talcite
So what is the actual chemical reaction that ends up breaking down organic matter?
Lots of them.
Alcohol tends to change the solubility of different proteins (due to alterations in the hydrogen bonding). There is therefore a tendency for proteins to coagulate and precipitate out of solution. (In the same way that cooking causes egg albumen to coagulate, and turn from a colourless, clear liquid into the characteristic white semi-solid 'white' - In fact if you drop an egg into 100% alcohol, the proteins will coagulate in much the same way).
Bleach, peroxide and other oxidisers, cause production of free radicals - these highly reactive intermediates will react will all manner of biological compounds, proteins, DNA, fats and oils,.
Detergents, (including quaternary ammonium compounds) tend to generally interfere with solubility in a similar way to alcohol.
Oh and why does alcohol not burn skin/our stomach linings or stuff like that then?
It does.
In the case of skin, the outer layers of the skin are dead cells which have turned into dry flakes of waterproof/solvent proof keratin. This keeps the delicate inner layers of the skin protected from the alchohol.
Hold neat alcohol in your mouth and it will burn it, or at least start causing the skin to blister and peel off.
You don't get 100% alcohol for drinking, and it will get diluted by the fluid in your stomach. And, the stomach is protected by a thick layer of mucus - and the lining continually replaces itself - so in general, you won't get much serious damage.
In the case of bleach, peroxide, or other chemicals, you can get severe burns of the mouth, oesophagus and stomach.
