In re: quinolone resistance

Steven_Projan at internetmail.pr.cyanamid.com Steven_Projan at internetmail.pr.cyanamid.com
Mon Oct 30 09:32:29 EST 1995

David.Shadick asks:

>Is resistance to quinolones, particularly ciprofloxacin, reversible?

Since resistance to fluoroquinolones are, for the most past, caused by 
chromosomal mutations (usually point mutations) in genes encoding gyrase, 
topoisomerase or efflux pumps (single and in combination) these mutations can 
revert (change back to the orignal DNA sequence and reassume the original, 
susceptible phenotype).

However the frequency with which such mutant strains revert after non-selective 
growth is not often reported in the literature.  David Hooper at Mass. Gen./
Harvard Med. indicated, in response to a question at a conference in San 
Francisco, that resistant strains retain their resistance phenotype even after 
non-selective growth.  I.e. reversion doesn't happen a lot.

Therefore, if the sense of the question is: Will ciprofloxacin resistant strains 

revert to susceptibility if we stop using fluoroquinolones?  The answer at this 
point is:  probably not.

Steve Projan
Wyeth-Ayerst Research

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