This is a good article that talks about the benefit of greater bacterial diversity -http://www.sciencedaily.com/releases/2011/12/111208114853.htm
This is also one of the laws of nature and a healthy ecosystem. The greater the variety of bacterial species, the greater the health of an ecosystem. An ecosystem with limited varieties of bacteria and other organisms is doomed to fail. This helps to reinforce the Hygiene Hypothesis that links many conditions to the aseptic world that we live in. This type of research has been going on for years. In another linked area, countries with greater exposure to parasites have fewer intestinal disorders like Irritable Bowl Syndrome, Crohn's, Colitis, etc.
The human intestinal tract contains 100 trillion bacteria, while the human body contains 10 trillion cells. Studies show that antibiotics permanently alter the healthy intestinal flora. Some studies show that one course of antibiotics will reduce the types of bacteria to just one species for months, and that one species is now antibiotic resistant.