Strain? isolate? - (Mar/06/2007 )

Dear all,

I am trying to analyse genetics distance of my collection of bacteria.
However I have little confusion:
1. what defines a strain and isolate?
2. what defines a reference strain?
3. is it a must that we set a reference strain in genetic distance studies?

thanks
Oche

1. A strain is a bacterium that has some level of genetic definition, often plasmids that confer specific traits. An isolate, by contrast does not necessarily have such definition, but is simply the bugs that were isolated from the sample.
2. A reference strain wold therefore be one that is hopefully well-defined, and is specifically used in an expt for comparing the isolated bacteria of the test.
3. I think it depends. There are situations where you are comparing relative distances, and some where you want to see how far a particular isolate has diverged from another, more constant strain. An example of this might be in bioremediation studies when you want to see if a bug that has been released into a polluted environment has become better-adapted, or has enlarged its range of energy source.