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Bacteroides fragilis

Microbiology > Bacteriology > Anaerobic bacteria > Gram-negative anaerobes
Bacteroides (B. fragilis, B. melaninogenica)
a.       Structure
                    i.      Bacteria: gram negative
                    ii.      Rod-shaped
b.      Pathobiology:
                    i.      Obligate anaerobe (can tolerate some air)
                    ii.      Variable motility dependent on the strain
                    iii.      Non-spore forming
                    iv.      Most common of the genus is Bacteroides fragilis.
c.       Epidemiology
                    i.      Normal component of the GI flora
                    ii.      Also found in the vagina in 60% of women
                    iii.      If given route into abdominal cavity (ex. Trauma, ulcer, surgery), it can cause intra-abdominal infection.
                    iv.      Not communicable
d.      Laboratory diagnosis
                    i.      Blood agar plates containing kanamycin and vancomycin
                    ii.      Identified by biochemical reactions and production of organic acids detected by gas chromatography
                   iii.     grows under anaerobic conditions
e.      Disease manifestations
                    i.      Most common cause of serious anaerobic infections
                    ii.      Causes peritonitis – inflammation of the peritoneum lining inner walls of the abdomen and covers most abdominal organs.
                    iii.      Most frequently associated with intra-abdominal infections – peritonitis or localized abscess.
                    iv.      May also see pelvic abscess, necrotizing fasciitis, and bacteremia
f.        Therapy
                    i.      Usual treatment is with metronidazole, carbapenems, tigecycline, or beta-lactam/beta-lactamase inhibitor.
                    ii.      Resistant to penicillins (because have beta-lactamase), macrolides, tetracyclines, and aminoglycosides
                    iii.      Among the most-resistant of anerobic bacteria.
                    iv.      Surgical drainage of abscess along with antibiotic therapy
g.       Prevention
                     i.      Perioperative administration of cephalosporin (often cefoxitin) before abdominal or pelvic surgery.
                     ii.      No vaccine available.
Related concepts

Key Words
1. Bacteroides
2. Gram-negative
3. Fragilis
4. Peritonitis
5. anaerobic

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