darwinian medicine

Michael F. Hynes hynes at acs.ucalgary.ca
Mon Oct 9 17:18:30 EST 1995

I also think that this is an interesting question. Some work along these 
lines has been done with plasmids and transposons and I believe some is 
discussed in one of the chapters in the book "Mobile DNA" edited by Berg 
et al. 

What I remember reading somewhere is that if you introduce a plasmid 
which codes for antibiotic resistance into a bacterium, then you can 
expect that replicating that plasmid will be costly in metabolic terms 
and that in the absence of selection, the plasmid will be lost. 
However, if you grow the bacterium in a chemostat for a lengthy period 
of time WITH selection, the plasmid seems to adapt itself to its new 
host, and be maintained afterwards without selection. 

Getting back to the original article, if the resistance was of the 
plasmid-encoded type, even if it dwindled to a small frequency in the 
population, it would rapidly increase as soon as the antibiotic was used 


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