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I know that bacteria can become resistant to antibiotics. Why do antiseptics like alcohols, PVP-I, still work on the strains of bacteria we have today? Shouldn't some bacteria have evolved to be resistant to them? I only hear about antibiotic resistance, so my assumption was that antiseptic resistance isn't a thing that happens. What fundamentally differentiates antibiotics and antiseptics so that antiseptics are not resistance-prone?

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For some classes of antiseptics the effect is more simple chemistry or even physics than biochemical toxicity. Ethanol will just denature proteins and dissolve the membrane, and the used concentration of ethanol is so high that no amount of efflux pumps is going to save the bacterium. Some other compounds work in a similar brute force way: QACs will break the membranes, hydrogen peroxide will just oxidize everything. For iodine (like in PVP-1) the mechanism is not really known, but probably it also just reacts with all kinds of things in/on the bacterial cell and kill them.

Antiseptic resistance could happen for some other antiseptics (or low concentrations of the compounds mentioned above). For some antibiotics, resistance is caused by the expression of efflux pumps that just pump out enough antibiotics so the cell survives. Bacteria could do the same for these antiseptics. The reason why it's not that much of an issue is that the application is rather different. Antibiotics are for inside use, antiseptics for topical use, you cannot just flood your whole body with 70% ethanol to kill all bacteria, but for a wound / something dirty this is just fine. This makes it much easier to avoid creating resistance.

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  • $\begingroup$ Please define and link to QACs. I know what they are, but many others will not, as it is not a common abbreviation, except possibly to chemists and certain microbiologists, as well as those who work in manufacturing. Overall, your post would benefit by several additional citations supporting your claims. $\endgroup$ – MattDMo Aug 29 '16 at 18:39
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Of course bacteria can evolve resistance against antiseptics. Usually antiseptics inflict direct damage to the cell rather than interfering in some biochemical pathway. Also, antiseptics are used in very high concentrations which usually leads to complete elimination of the microbes. Moreover, different antiseptic/disinfectant agents have different toxicity to different organisms; for example anaerobic bacteria are more sensitive to oxidizing agents like hydrogen peroxide and potassium permanganate.

There are bacteria (Deinococcus radiodurans) and fungi that are even tolerant to ionizing radiation like gamma rays.

There are other extremophiles too which thrive in extreme physical/chemical environments (extreme heat/pH/salinity/pressure etc).

For more information on antibiotics vs antiseptics see this post: Why is triclosan not considered an antibiotic?

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