Bacteroides fragilis

Please note: This is for information only.

Refer to local guidelines for treatment recommendations



  • A Gram-negative bacillus that only grows anaerobically.
  • Commonest anaerobe isolated from clinical specimens.

Main Clinical Infections

  • Intra-abdominal infections and soft tissue infections below the waist.
  • Most common anaerobe found in bacteraemia, often as part of polymicrobial sepsis.

Usually Sensitive to:

  • Metronidazole
  • Co-amoxiclav
  • Meropenem / Imipenem
  • Piptazobactam (Tazocin®)
  • Clindamycin

Usually resistant to:

  • Benzylpenicillin (due to b-lactamase production)
  • Amoxicillin
  • Cefuroxime
  • Gentamicin
  • Quinolones (Ciprofloxacin, levofloxacin)
  • Macrolides (Erythromycin, clarithromycin)