Read condition-specific symptoms and clinical context for Bacteroides fragilis. A small share of the gut community that helps ferment carbohydrates, and the anaerobe most often isolated from infections.
Wexler’s review describes the human colon as the largest bacterial population in the body, in excess of 10 to the 11th organisms per gram of wet weight, of which about 25% are Bacteroides species. B. fragilis itself accounts for only 0.5% of the colonic flora yet is the most commonly isolated anaerobic pathogen. In the gut, carbohydrate fermentation by Bacteroides produces volatile fatty acids that the host reabsorbs and uses as an energy source. When it escapes the gut it causes abscesses and bacteraemia; PHAC notes that spread to the bloodstream is more common for B. fragilis than for any other anaerobe.
One possible infection setting for this organism. These are general syndrome symptoms, not signs that identify the bacterium. Other infection sites can present differently.
Possible symptoms: Persistent abdominal pain; Fever or chills; Nausea or reduced appetite.
Seek medical assessment for severe abdominal pain, fever or persistent vomiting.
Presence at a normal body site does not by itself establish disease.
No infection symptoms are assigned to ordinary carriage. Clinical assessment distinguishes colonization from infection.
This app cannot determine whether a person has an infection.
Source check: 2026-09-19. Educational content; independent scientific review remains pending.