Bacteroides fragilis

from Wikipedia, the free encyclopedia
Bacteroides fragilis
Bacteroides fragilis (Gram stain)

Bacteroides fragilis (Gram stain)

Department : Bacteroidetes
Class : Bacteroidia
Order : Bacteroidales
Family : Bacteroidaceae
Genre : Bacteroides
Type : Bacteroides fragilis
Scientific name
Bacteroides fragilis
( Veillon & Zuber 1898)
Castellani & Chalmers 1919

Bacteroides fragilis , like the other members of the genus Bacteroides , belongs to the gram-negative , obligately anaerobic and non- spore-forming rod-shaped bacteria. Bacteroides spec. belong in particular as intestinal germs to the physiological flora of humans and animals. As part of this flora, the bacterium plays an important role in the so-called colonization resistance . Bacteroides fragilis is often found in mixed infections with aerobic or facultative anaerobic bacteria.


Bacteroides fragilis is relatively sensitive to oxygen . The bacteria are gel-resistant, break down sucrose and are not pigmented. Bacteroides fragilis forms z. Sometimes a capsule that protects the bacterium from phagocytosis in combination with other anti-phagocytic substances . The lipopolysaccharide (LPS) of Bacteroides fragilis differs from that of the aerobic bacteria and has a lower toxicity in the host organism. Bacteroides fragilis has fimbriae to improve adherence and produces various ectotoxins .

As a special feature it should be noted that 79% of all fatty acid chains occurring in the bacterium are branched.

Diseases caused

Bacteroides fragilis and Bacteroides thetaiotaomicron are often found in mixed infections, e.g. B. in peritonitis , gynecological infections (e.g. adnexitis ), intra-abdominal abscesses , aspiration pneumonia , sinusitis and brain abscesses .

The Bacteroides fragilis group can also be involved in other intra-abdominal infections as well as in ulcus cruris and diabetic foot syndrome. Bacteremia or sepsis also rarely occur.


Bacteroides fragilis is not one of the typical environmental germs. Rather, it belongs to the normal human bacterial flora.


The colonization of humans by Bacteroides spec. usually takes place during the first few years of life. Infections are therefore mostly endogenous, that is, they start from the physiological flora of the own body.


About 5–10% of sepsis cases caused by gram-negative rods are due to infections caused by Bacteroides spec. back. Bacteroides fragilis is the most common isolated germ of the Bacteroides . Bacteroides spec . Are also often found in intra-abdominal infections .

Incubation period

The incubation period is usually only two to six days.


As part of the physiological flora, Bacteroides fragilis is not pathogenic . Infections result from the spread of germs into actually sterile areas of the body. An infection often occurs initially through aerobic or facultative anaerobic bacteria. These lower the partial pressure of oxygen in the infected tissue. Only now do Bacteroides spec. the source of infection. Bacterial isolates from sources of infection usually form a capsule, which, however, is often no longer found after several subculture steps.


  • Cultivation: Bacteroides fragilis can be cultivated under strictly anaerobic conditions on special culture media. After two days, bacteria of the Bacteroides fraglilis group usually form 1–3 mm large, shiny gray colonies . To differentiate the Bacteroides fragilis group, biochemical or gas chromatographic tests are necessary.
  • Microscopy : Gram staining and staining with group-specific fluorescence- labeled antibodies can confirm the diagnosis.


Necroses and abscesses usually have to be tackled and repaired surgically, as antibiotics often do not penetrate the infected area in sufficient quantities. Against aminoglycosides are Bacteroides primarily resistant. Lactamase-sensitive penicillins and cephalosporins are often destroyed by potent β-lactamases . Therefore v. a. Nitroimidazoles (e.g. metronidazole ), clindamycin , carbapenems (e.g. imipenem ), as well as aminopenicillins ( amoxicillin ) or acylaminopenicillins ( piperacillin ) each together with β-lactamase inhibitors ( clavulanic acid or tazobactam ). Also tigecycline can be used as an alternative. The corresponding antibiotics are usually used if there is a suspicion, as bacteriological diagnostics often take too long.


In 1898, Veillon and Zuber described Bacteroides fragilis (at that time still Bacillus fragilis ) for the first time as a causative agent of appendicitis .

Individual evidence

  1. T. Kaneda: Iso- and anteiso-fatty acids in bacteria: biosynthesis, function, and taxonomic significance. In: Microbiol. Rev. 55 (2); June 1991: pp. 288–302 PMID 1886522 (free full text access )
  2. ^ Marianne Abele-Horn: Antimicrobial Therapy. Decision support for the treatment and prophylaxis of infectious diseases. With the collaboration of Werner Heinz, Hartwig Klinker, Johann Schurz and August Stich, 2nd, revised and expanded edition. Peter Wiehl, Marburg 2009, ISBN 978-3-927219-14-4 , p. 261.