Bacteroides fragilis

Bacteroides fragilis is an anaerobic, Gram-negative, rod-shaped bacterium that belongs to the Bacteroidaceae family.

Infections involving Bacteroides fragilis are often mixed aerobic–anaerobic infections.

Mixed anaerobic infections can occur when the normal flora colonized by anaerobic microorganisms (including mucous membranes of the mouth or gastrointestinal tract) is disturbed, for example, by surgery or injury.

Bacteroides fragilis causes the following disease patterns:

  • Perforation and wound infections

  • Peritonitis (inflammation of the peritoneum)

  • Appendicitis (inflammation of the vermiform appendix)

  • Gynecological infections

  • Aspiration pneumonia

  • Abscesses

Bacteroides fragilis belongs to the normal bacterial flora of humans and animals, especially as an intestinal germ.

Relevance of pathogen in transmission in endoscopy

  • Gastroenterology: High

  • Pulmonology: Low

  • Ear, nose, and throat: Not relevant

  • Urology: Low

Relevance for endoscope surveillance*

  • High concern organism

Transmission route

Human colonization by Bacteroides fragilis often occurs during the first years of life. Infections are therefore mostly endogenous.

Resistance to antibiotics

Bacteroides fragilis have a pronounced antibiotic resistance, especially to beta-lactam antibiotics and also to aminoglycosides and tetracyclines.

Sources and further readings

  1. Bacteroides spp., Infektionsnetz Österreich, Accessed on 06.29.2021.

  2. Gries O, Ly T: Infektologie – Kompendium humanpathogener Infektionskrankheiten und Erreger, Springer-Verlag Berlin Heidelberg 2019.

  3. Multidrug-Resistant Bacteroides fragilis, Centers for Disease Control and Prevention, Accessed on 06.29.2021.

  4. Nelson DB. 2003. Infection control during gastrointestinal endoscopy. J. Lab. Clin. Med. 141:159–167.

* This bacterium is anaerobic, so it does not grow on surveillance agar (relevant e.g., in outbreak situations).