Scott Hoffman (schoffma at badlands.nodak.edu) writes:
> If a population of vancomycin resistant cells were selected for by
> vancomycin treatment, and then the selective pressure of vancomycin was
> removed, would it be resonable to believe that a population of vancomycin
> sensitive cells would eventually outcompete and re-establish itself? As
[snip]
I think this is a very good question. As Scott says, if
unselected antibiotic resistance involves a metabolic cost, then
one would expect it to disappear from the population quite
quickly, but if the gene is repressed and presents essentially
no cost, then what?
I think the key to this is the probability of (selectively neutral)
mutation in the gene during the period of no selection by
antibiotic. Given an estimate of mutation rate, and a starting
population of resistant bacteria, their growth and death rate
etc. I guess it would be possible to calculate the likely
distribution of bacteria remaining after time t with no, one,
two etc. mutations.
My guess is that a population of cells carrying a single muation
would give rise to resistant clones almost immediately when
antibiotic selection is re-imposed, but there must be a number
of mutations for which this probability drops effectivley to
zero. One should be able to determine this experimentally.
Maybe someone has already? What do y'all think out there?
----------------------------------------------------------------------
Walter Ogston ogston at hobbes.kzoo.edu
Department of Biology Phone: (616)337-7010
Kalamazoo College Fax: (616)337-7251
Kalamazoo, MI 49006-3295
