Re: Evolutionary selection technique to combat 'Superbugs'

I think there are a few gaps in your understanding about how this works.
The bacteria are resistant to antibiotics because they've either evolved or
more likely been transformed with genes from other bacteria that make them
able to live in the presence of antibiotics.  Your use of the word
"combative" is one I've not heard before and I don't understand what you
mean with it. 

These resistant bacteria- for example MRSA, attack human and animal hosts.
I am unaware of their antagonism towards other bacteria. Actually certain
other (often non-pathogenic) bacteria antagonise Staph and other pathogens.

I'm confused as to how you think this would work and what you mean by it: 

"Could new treatments be discovered by using the superbugs themselves to
destroy colonies of otherwise harmless bacteria, acting as a selector for any
resistance-conferring mutations that may arise, which could then be used to
develop a new treatment?"