His research interests include the epidemiology and prevention of CDI, antimicrobial resistance, and antimicrobial distribution and kinetics. He has been a Merit Review funded research investigator in the VA for over 40 years and is the author of over 400 peer-reviewed journal publications, book chapters, and review articles. He holds patents and technology for the use of non-toxigenic C. difficile for the prevention and treatment of this disease. He is a member of the editorial boards of Clinical Infectious Diseases, Antimicrobial Agents and Chemotherapy, Gut Microbes, and Infection Control and Hospital Epidemiology, and is a reviewer for numerous other medical journals.