[thedoc (OP)]

Ed Wilson  asked the Naked Scientists:
   
The genome of a bacterium is flexible, perhaps, but it is finite.  As bugs evolve resistance to new chemicals, is it possible that resistance to older drugs - particularly those no longer in the environment - may be disrupted or lost?

Ed Wilson

What do you think?

[chris]

Yes; bacteria acquire from other microbes DNA elements that encode resistance factors. These are positively selected by the presence of antimicrobial compounds. But if this selective pressure is removed then the function of the resistance elements may be lost or discarded because it is energetically unfavourable to maintain it. Consequently, bacteria can evolve to become sensitive to a compound again.

[DaveC]

One of the methods if combating antibiotic resistance would be to remove certain antibiotics from general use, reintroducing them decades later. As a rolling program this would help and perhaps pharmaceutical companies would not have the same pressure to develop new antibiotics. Of course the patents on these old, stored and later reintroduced antibiotics would have long expired...so not much incentive to do this is there.