Properties

Pathogenesis

Clinical findings

Laboratory diagnosis

Treatment & Prevention

Anaerobic

Non-spore forming

Gram-negative rods

B.fragilis are the predominant organisms in the human colon.

Infections are endogenous, arising from a break in a mucosal surface, & are not communicable.

Organisms cause a variety of infections:

- local abscesses at the site of a mucosal break.

- metastatic abscesses by hematogenous spread to distant organs.

- lung abscesses by aspiration of oral flora.

Predisposing factors:

- surgery

- trauma

- chronic disease

Local tissue necrosis, impaired blood supply, & growth of facultative anaerobes at site contribute to anaerobic infections.

Polysaccharide capsule is an important virulence factor.

Most common cause of serious anaerobic infections:

- sepsis

- peritonitis

- abscesses

Pelvic abscesses & bacteremia occur as well.

Isolated anaerobically on blood agar plates containing kanamycin & vancomycin to inhibit unwanted organisms.

Identified by:

- biochemical reactions (sugar fermentation).

- production of certain organic acids (formic, acetic acids).

Resistant to:

- penicillins

- first-generation cephalosporins

- aminoglycosides

Penicillin resistance is the result of beta-lactamase production.

Choice of drug:

- metronidazole

- cefoxitin

- clindamycin

- chloramphenicol

Aminoglycosides are frequently combined to treat the facultative gram-negative rods in mixed infections.

Surgical drainage of abscesses usually accompanies antibiotic therapy, but lung abscesses heal without drainage.

Prevention: perioperative administration of a cephalosporin, frequently cefoxitin, for abdominal or pelvic surgery.