MedicalResearch.com Interview with Frederic D. Bushman, Ph.D. Professor, Department of Microbiology Department of Microbiology Perelman School of Medicine University of Pennsylvania 426A Johnson Pavilion 3610 Hamilton Walk Philadelphia, PA 19104   MedicalResearch.com: What are the main findings of the study? Dr. Bushman: Viral populations in the human gut are huge, and some of the viruses change rapidly over time.