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In its FAQ, the company states:

Does Purell® instant hand sanitizer contribute to antimicrobial resistance?

No, because alcohol evaporates completely, there is no alcohol left behind to promote adaptation. Alcohol has been used in health care for many years with minimal adverse effects.

This reasoning seems questionable. Does ethyl alcohol -- not to mention Purell's other ingredients (Isopropyl myristate, in particular, is concerning) -- not apply selective pressure to germs, killing off those most susceptible to Purell and thus clearing the way for the proliferation of competing "superbugs"?

Am I misunderstanding antimicrobial (antibiotic) resistance?

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    This is the first time I’ve heard alcohol referred to as an antibiotic and I believe that this isn’t a common usage. That said, nothing in the (imprecise and arbitrary) usual definition of “antibiotic” actually contradicts the usage so I’m letting it stand. – Konrad Rudolph Aug 13 '12 at 15:40
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    I assume what they meant to say was: "The alcohol evaporates completely. Any microbes that have evolved expensive mechanisms to offer partial resistance to alcohol must then compete with air-borne newcomers without such expensive mechanisms, and will tend to be out-bred. With Purell's competitors that contain triclosan or similar, the agent remains, allowing any resistance to thrive in the absence of competitors." Not saying this argument is right, but it is more reasonable. – Oddthinking Aug 14 '12 at 13:57
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It is true that bacteria can't become resistant to ethanol to our current knowledge, but the cited reason doesn't sound plausible to me.

According to "Epidemiologic background of hand hygiene and evaluation of the most important agents for scrubs and rubs." published in Clinical Microbiology Reviews in 2004:

No acquired resistance to ethanol, isopropanol, or n-propanol has been reported to date.

If you compare the mechanism of alcohols with antibiotics, the reason for that is pretty plausible. Antibiotics like penicillin bind to specific proteins and disrupt their function, in the case of penicillin those are proteins that are responsible for building the cell walls. The bacteria can evolve a resistance to such antibiotics e.g. by changing the shape of the target protein in a way that reduces binding of the antibiotic, by creating a transporter that removes the antibiotic, or in the case of beta-lactam antibiotics like penicillin by creating an enzyme that inactivates those antibiotics.

Those mechanisms would not work for ethanol. The mechanism of ethanol is unspecific:

Alcohols have a nonspecific mode of action, consisting mainly of denaturation and coagulation of proteins (241). Cells are lysed (229, 428), and the cellular metabolism is disrupted (360).

There are no obvious ways to resist those effects, they are based on the fundamental chemistry of living organisms as we know them.

  • Which would mean it's having the same effect on whoever it's applied to, right? Just at a level that doesn't 'do' much, given size differences (a person is made of many cells, thankfully). – Clockwork-Muse Aug 13 '12 at 19:52
  • Alcohol has been used for thousands of years to preserve beer and wine, and still seems to work well in that role at present. That seems to preclude any resistance to it by micro-organisms. – hdhondt Aug 14 '12 at 3:39
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    I wonder why they discount these examples of alcohol resistance? 1, 2 – Oddthinking Aug 14 '12 at 13:49
  • @Oddthinking Interesting case, it's somewhat different from the usual antibiotic resistances as those bacteria still can't survive alcohol, they just take a bit longer to die. – Mad Scientist Aug 14 '12 at 14:00
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    This answer seems pretty right on. Although the Purell explanation is lacking, I can't find any credible evidence that any bacteria can survive exposure to ethanol -- at least one individual must survive if evolution (resistance) is to develop. In fact, Purell hints at what might be the best evidence against alcohol-resistant bacteria: history. Despite hundreds of years of medicinal alcohol use, no evidence of resistance has arisen. That's a pretty rigorous experiment. Of course, that experiment didn't involve Purell's other ingredients... – samthebrand Aug 14 '12 at 15:38

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