Updated: 4/20/2020

Bacteroides fragilis

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Topic
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
  • Death
  • Contiguous spread of infection

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Questions (1)

(M1.MC.15.75) A 36-year-old male suffered a gun-shot wound to the abdomen that required an emergent exploratory laparotomy to repair and resect damaged portions of the bowel. Four days later, the patient reports increased generalized abdominal pain. His vital signs are as follows: T 38.5, HR 110, BP 110/60, RR 18, SpO2 96%. Physical exam reveals extreme tenderness to palpation of the abdomen as well as rebound tenderness, worse in the bilateral lower quadrants. The abdomen is mildly distended with guarding and decreased bowel sounds. The surgical and bullet-entrance wounds appear intact without any evidence of leakage/drainage, erythema, or warmth. Initial lab-work shows an elevated white blood cell count of 17.1 x 10^9 cells/L. A CT scan of the abdomen shows a 4 cm abscess in the left lower quadrant. Which of the following organisms is the most likely cause of this patient's current presentation? Tested Concept

QID: 106739
1

Pseudomonas aeruginosa

29%

(10/35)

2

Salmonella enteritidis

0%

(0/35)

3

Bacteroides fragilis

51%

(18/35)

4

Enterococcus species

11%

(4/35)

5

Streptococcus bovis

6%

(2/35)

M 2 C

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Evidence (1)
EXPERT COMMENTS (2)
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