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I wonder why bacteria and fungi cannot develop resistance and mutate agains essential oils?

For example, some fungi get killed by oregano oil.

Being not a biologist, I hope my question is not so stupid..

Thank you!

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  • $\begingroup$ Can you cite a specific example? For any given fruit or plant, I'm sure there is at least one fungus or bacterium that can colonize it successfully. $\endgroup$ – Superbest Sep 6 '14 at 23:40
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Here are my thoughts on this, taking your example, oregano oil.

The active anti-microbial ingredient in this essential oil is carvacrol. The WP article states that it probably acts by disruption of the membrane. There appear to be no examples of carvacrol resistance, as suggested by your question. In mammals the compound is detoxified in the liver via esterification to increase solubilty, thus promoting excretion.

Assuming that we can create a situation with a strong selective pressure for the development of resistance in a microbe, what would that resistance look like? If the carvacrol does indeed disrupt the membrane, then it is probably useless to develop intracellular degradation - what is needed is the secretion of an enzyme that is able to inactivate the compound, analogous to the β-lactamases that inactivate antibiotics like penicillin (which also has an extracellular mode of activity).

Furthermore, unlike β-lactams, carvacrol is insoluble in water. This suggests to me that most of the time, in the natural environment, free-living bacteria will not experience significant levels of the compound.

In summary - it may be difficult to evolve a system for the degradation of a lipophilic compound, and because it is lipophilic it may be that it is rarely a problem for bacteria unless they are being subjected to laboratory tests for antimicrobial activity.

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