Research in my lab has involved investigations of the human biota as well as exploration of the genetic diversity of bacteria in general. Much of our work has focused on Clostridium difficile, the agent of antibiotic associated colitis. We showed that this intestinal pathogen is suppressed by the colonic biota, and were able to simulate suppression in gnotobiotic mice by colonizing them with a complex collection of bacteria isolated from the normal mouse cecum. It was also possible to show that normal bacteria suppressed C. difficile by competing more efficiently for carbohydrates found in the gut. Work with C. difficile continues with a small collection of fastidious organisms from human biota that exert a powerful suppressive effect. Other work has included description of the molecular phylogeny of the (then) uncultured Whipple bacillus and the first molecular typing system able to different strains of anthrax. More recently we have reported development of a photolithography chip containing 31,000 oligonucleotide probes directed at ribosomal DNA sequences for identification of life forms. Current work in the lab involves studies of the genetic diversity of components of human biota colonizing individuals at different geographic sites. We are also studying the composition of the intestinal biota in subjects with inflammatory bowel disease.