Bacteroides fragilis (IMAGE) Marine Biological Laboratory Caption B. fragilis is a commensal bacteria that normally lives in the human gastrointestinal tract. It can become pathogenic due to disruption of the normal intestinal mucosa through trauma or surgery. Credit: Centers for Disease Control/V.R. Dowell Jr. Credit Credit: Centers for Disease Control/V.R. Dowell Jr. Usage Restrictions No restrictions. License Public Domain Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.