darwinian medicine

Walter Ogston ogston at HOBBES.KZOO.EDU
Fri Oct 13 12:44:58 EST 1995


Shan Putnam (sputnam at tbf.com) writes: 
> 
> I just finished reading Dr. Stuart Levy's book "The Antibiotic 
> Paradox" and he addresses this very issue (p 245-246).  
> Apparently the literature doesn't support the "remove the 
> antibiotic -- lose the resistance."  He states "Since this 
> perstistence is not associated with the constant presence of an 
> antibiotic, it presumably relates to other features of the 
> resistance phenomenon."  ie.) antibiotic resistance determinants 
> (whether plasmid mediatated or chromosomal) participating in 
> heavy metal resistance.  

I won't argue with the observation that antibiotic resistance
genes persist in the absence of apparent selection.  The
question is how long?  The life time of an unselected gene based
on the approximately known mutation rates for bacterial DNA
replication must be thousands of generations or more (I haven't
done the calculation, I am guessing, so don't flame me if I am
out by orders of magnitude).  How long were the experiments
cited by Levy carried on for.  

The other possibility, that the same genes are pleiotropic and
code for heavy metal resistance is interesting.  Is there any
evidence for it?  And in the experiments or natural observations
is selection by heavy metals known to operate?  
----------------------------------------------------------------------
Walter Ogston				ogston at hobbes.kzoo.edu
Department of Biology			Phone: (616)337-7010
Kalamazoo College			Fax:   (616)337-7251
Kalamazoo, MI 49006-3295



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