Several years ago, my dermatologist identified my digestive system bacterial and function issues using a kit provided by Great Smokies diagnostics Labs. You can still have this done through the mail by the same company which is now called Genova Diagnostics http://www.gdx.net/
They can perform a Comprehensive Digestive Stool Analysis 2.0ô (CDSA 2.0)
I was sick before I had this done, and the results confirmed it. Staph Aureus, Candida Parapsilosis & undigested fats among many other things that I can't recall right now, but I can dig out the full report if necessary.