Bacteroides fragilis

Bacteroides fragilis ( Gram stain )

Bacteroides fragilis heard how the other members of the genus Bacteroides, to the gram-negative, obligate anaerobic and non-spore- forming rod bacteria. Bacteroides spp. belong to the physiological flora of humans and animals. As part of this flora the bacteria have an important role to play in the so-called colonization resistance. Bacteroides fragilis is often found in mixed infections with aerobic and facultative anaerobic bacteria.

Properties

Bacteroides fragilis reacts to oxygen relatively sensitive. The bacteria are resistant to bile, cleave sucrose and are not pigmented. Bacteroides fragilis is partly a capsule that protects the bacteria in combination with other anti- phagocytic substances prior to phagocytosis. Lipopolysaccharide (LPS) from Bacteroides fragilis is different from that of the aerobic bacteria and exhibits a lower toxicity in the host organism. Bacteroides fragilis has to improve adherence fimbriae and produces different Ektotoxine.

A special feature to be noted that 79% of all bacteria occurring in the fatty acid chains are branched.

Diseases caused

Bacteroides fragilis and Bacteroides thetaiotaomicron are often found in mixed infections, such as peritonitis, gynecological infections (eg pelvic inflammatory disease ), intra-abdominal abscess, aspiration pneumonia, sinusitis and brain abscess.

Spread

Bacteroides fragilis is not one of the typical environmental pathogens. Rather, it is part of the normal bacterial flora of humans.

Transmission

The settlement of the people by Bacteroides spp. usually takes place during the first years of life. Infections are therefore mostly endogenous, ie starting from the physiological flora of one's body.

Frequency

Approximately 5-10% of sepsis cases are caused by gram -negative rods, go on infections caused by Bacteroides spp. back. Bacteroides fragilis is the most frequent isolated germ of Bacteroides. In intra-abdominal infections are also common spec Bacteroides.

Incubation

The incubation period is usually only two to six days.

Pathogenesis

As part of the physiological flora Bacteroides fragilis is not pathogenic. Infections caused by germs in actually sterile areas of the body. Frequently, first a infection by aerobic or facultative anaerobic bacteria. These reduce the oxygen partial pressure in the infected tissue. Only now infecting Bacteroides spp. the infection. Bacterial isolates from infected herds usually form a capsule which often are not found after several subculture steps.

Diagnostics

• Cultivation: Bacteroides fragilis can be cultured on special media under strictly anaerobic conditions. After two days the bacteria Bacteroides fraglilis group usually form 1-3 mm, gray - shiny colonies. For the differentiation of Bacteroides fragilis group biochemical and gas chromatographic investigations are necessary.
• Microscopy: The Gram staining and staining with group-specific fluorescent - labeled antibodies can confirm the diagnosis.

Therapy

Necrosis and abscesses usually have to be surgically addressed and redeveloped as antibiotics usually do not penetrate into the infected area in sufficient quantity. Aminoglycosides against Bacteroides are primarily resistant. Lactamase sensitive penicillins and cephalosporins are often destroyed by potent β -lactamases. For use therefore come V.A. Nitroimidazoles (e.g. metronidazole ), clindamycin, carbapenems (e.g. imipenem ) and aminopenicillins ( amoxicillin ) and acylaminopenicillins ( piperacillin ) in each case together with β -lactamase inhibitors ( clavulanic acid or tazobactam ). The appropriate antibiotics are usually already in suspected used, since the bacteriological diagnosis often takes too long. In operations in the intestinal tract chemoprophylaxis is often performed to prevent an infection caused by anaerobes.

Historical

Veillon and Zuber described in 1898 Bacteroides fragilis (then Bacillus fragilis ) for the first time as the causative agent of appendicitis.