Bacteroides fragilis

Snapshot

A 25-year-old man presents to the emergency room for pain in his right lower quadrant. He was found to have perforated appendicitis and was immediately taken to the operating room for emergent laparoscopic appendectomy. Due to the complexity of the case, the operation was converted to an open appendectomy. Post-operatively, he was put on a 7-day course of clindamycin and returned home. Two days later, he returned to the emergency room for diffuse abdominal pain. A computed tomography (CT) of his abdomen shows a fluid collection at the site of the appendix.

Introduction

Classification
- Bacteroides fragilis
  - an anaerobic, gram-negative bacillus
  - part of the bacterial flora of the mucous membranes including gastrointestinal tract, mouth, and genitals
  - can cause abscesses at any endogenous site, including central nervous system (CNS), head and neck, abdomen, and pelvis
Epidemiology
- incidence
  - more common in chronic infections
- risk factors
  - immunocompromised state
  - bad dental hygiene
  - animal bite
  - trauma
  - surgery
Pathogenesis
- susceptible to oxidative damage
- capsule is antiphagocytic
penicillin resistance due to beta-lactamase production

Presentation

CNS infections
- brain abscess
Head and neck infections
- dental infection
- retropharyngeal abscess
- peritonsillar abscess
Aspiration pneumonia
Empyema
Intra-abdominal infections
- peritonitis
- abscess
Wound infections

Imaging

Computed tomography (CT)
- site
  - involved area (i.e., abdomen)
- indication
evaluate for abscess

Studies

Labs
- anaerobic culture
Making the diagnosis
most cases are diagnosed based on clinical findings, imaging, and laboratory studies

Differential

Necrotizing fasciitis
- distinguishing factors
  - often also caused by anaerobic bacteria producing gas
infection of fascia and presents with pain out of proportion to exam

Treatment

Management approach
- the ultimate choice of antibiotic therapy depends on cultured bacteria and its sensitivity profile
- antibiotics shown below are commonly used against anaerobes
Medical
- metronidazole
  - indication
    - good activity against anaerobes
    - limited activity against aerobic bacteria
- clindamycin
  - indication
    - B. fragilis is becoming increasingly resistant
    - activity against aerobic, gram-positive cocci as well
Operative
- surgical incision and drainage of abscesses
  - indication
abscess

Complications