This sounds rather drastic but take a look at this site.
If it is pathogens we want to kill and assuming any gets down to the colon/rectum
this will kill them.
Check out curezone they are starting to do it there for various health problems.
I know of one Crohns person who says he is now in remission from this.
Of couse this could be real hard on the gut, some get sick and the runs from it.
The chemistry is valid and is as indicated on the site.
As soon as I can get some I will give it a trial, for my UC of the past 27 years.